One and only one is Bhagavaan or Paramaatmaa (God). In Hindu philosophy it is called "Adwaitvaad" - when you believe in one supreme power and only one supreme power.

There are three letters in AUM - A, U, M.

There are three "Lok" (Worlds) - Dev Lok (where gods live), Mrityu Lok (this Earth), and Paataal Lok (where the Naag - snakes - and other lower species live). Dev Lok is above the sky, Mrityu Lok is this Prithvi Lok (the Earth), and the Paataal Lok is below this Earth.

There are three Gun (attributes) Sat, Raj, and Tam. Sato Gun has all the good qualities, is pious and noble - only gods have that kind of nature. Rajo Gun has mixed qualities - some good and bad. These are Maanav (human beings) who have this nature. Tamo Gun has almost all the bad qualities - and these are Raakshas or Asur (demons).

There are three types of foods - Sato Gunee food or Saatwik food, Rajo Gunee food or Raajas food and Tamo Gunee food or Taamasik food.

Sato Gunee food includes fresh fruits and vegetables, milk, yogurt, fresh simple food without much spices, sweets, Ghee (purified butter) etc. This type of food is liked by gods and helps in maintaining good qualities, cultivate good habits and sweet nature in a person.

Rajo Gunee food includes mixed type of food, some Sato Gunee and some Tamo Gunee food. In this kind of food also, if the quantity of Saatvik food is more then a person will have more good qualities. Rajo Gunee food includes sweets, fried food, very tasty food, spicy food etc.

Tamo Gunee food includes: meat, fish, long-kept food, alcohol, pickles etc. This type of food is liked by Asur (Demons) and it develops bad nature in a person. The person becomes sinful, angry, lusty and greedy by eating such foods.

In Vedanta, the 3 Gunas make up Nature!( Satwas, Rajas & Thamas).

Holistic Medicine or AyurVeda is built upon the theory of the 3 humours (Vata, Pitta & Kapha).

A Trikone (Triangle) has three sides.

A Cube has three dimensions.

In North India on some festivals, a certain amount of food is taken out, and is given to elders, normally to in-laws and their family members. It is called Baayanaa. When this food is taken out, women circumambulate it three times with water and some money in hand.

For example, when women do Chandra (Moon) Poojaa, and Taaraa (star) Pooja on Karavaa Chauth, or Poornmaasee (Full Moon day), or on Hoyee Ashtamee day, they offer water, flowers, Rolee, rice etc. to Chandra Devtaa and Taaraa only three times, and take out the Baayanaa by circling that food with some money and water three times only.

There are four Yug: Sat Yug, Tretaa Yug, Dwaapar Yug, and Kali Yug (now we are in Kali Yug). Do you know how many years are in each Yug? Each Yug has different number of years and all ofd them jointly are called a Mahaayug:

Sat Yug        = 1,728,000  years
Tretaa Yug    =  1,296,000 years
Dwaapar Yug =    864,000 years
Kali Yug        =    432,000 years
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                       4,320,000 = 1 Chaturyug or 1 Mahaayug

There are four Ved - Rig Ved, Yajur Ved, Atharv Ved, and Saam Ved. Among them Rig Ved contains verses of God's praise. Yajur Ved contains verses related to Yagya and gods worship. Atharv Ved contains verses related to Tantra Vidyaa (magic). Saam Ved contains verses related to music.

There are four Seasons in Temperate Regions - Winter (Dec 21 - Mar 21), Spring (Mar 21 - Jun 21), Summer (Jun 21 - Sep 21), and Fall or Autumn (Sep 21 - Dec 21).

At 40 degree North of Equator, on December 21, the shortest day of the year is only 10 hours long and the night is 14 hours long. On the contrary, on Jun 21, the longest day of the year is 17 hours long and the night is 7 hours long only.

There are four Aashram in a person's life. These Aashram are based on the age of 100 years.

(1) Brahmcharya Aashram - (Up to 25 years of age) - In this Aashram the person is a child and he earns the knowledge to use it in the world in Grahasth Aashram. He goes to a Guru after 5 or 7 years of age, and stays there to learn the style of living in the world.

(2) Grihasth Aashram - (25 years of age to 50 years of age) - This is the most important Aashram of the life as the person gets all kinds of opportunities to do many things only during this period. After earning knowledge, he returns to the world, marries and produce children. In this Aashram, the person performs all his duties related to family and pays all the Rin (debts) - Pitra Rin, Dev Rin, and Brahm Rin. The Pitra Rin is paid by offering food to the dead Poorvaj (Pitar or dead elders). Dev Rin is paid by doing Yagya and Havan etc. and by donating worldly things. And Brahm Rin is paid by producing children.

(3) Vaanprasth Aashram - (50 years of age to 75 years of age) - In this Aashram the person tries to detach himself from the worldly things and spends more time in worship and meditation. This he does living in the world with his family but detaching himself from the world gradually.

(4) Sanyaas Aashram - (75 years of age to 100 years of age) In this Aashram, he leaves the world and his family and goes in the forest to worship, meditation and Tapasyaa (penance). During this period he passes his time in preparing to meet Paramaatmaa.,

There are four Varn (castes) - Braahman, Kshatriya, aishya and Shoodra. Each Varn has its specific duties in the society.

All the latter three Varn take help of Braahman to fulfill their Grahasth Aashram duties - Yagya, donation etc.

Vedic Astrology is an indispensable tool for achieving, what the Vedas proclaim as the four-fold goals of human existence :-

• Dharm - Life Purpose, duties
• Arth    - Prosperity, related to wealth
• Kaam  - Pleasure
• Moksh - Spiritual Liberation

A rectangle and a square have four sides too.

Four holy abodes (Dhaam) - Badareenaath in north, Puree in east, Raameshwaram in south, and Dwaarakaa in west. But they are incomplete if Pushkarjee is not visited in the last.

Five Gyaan Indriyaan, out of eleven Indriyaan, are main in our body, that is our five Gyaan Indriyaan through which we earn knowledge and serve Bhagavaan (God). Eyes - by seeing Bhagavaan, ears - by hearing Bhagavaan's praise, nose - by smelling Bhagavaan's presence, skin - by touching Bhagavaan's Swaroop (Form), tongue - by pronouncing Bhagavaan's word.

There are five Karm Indriyaan - hands to work, feet to walk, reproduction organ for producing children, excreting organ to remove waste, and tongue to speak.

There are five mothers - Gaayatree, Tulasee, Gangaa, Kaamdhenu, and Arundhatee (Vashishth's wife).

There are five maidens or Satee - Ahalyaa Gautam's wife), Draupadee (Paandav's wife), Seetaa (Raam's wife), Taaraa (Baali's wife), and Mandodaree (Raavan's wife).

There are five Devee (goddesses) - Umaa (Shiv's wife), Ushaa (goddess of dawn), Vaidehee (Raam's wife), Ramaa (Vishnu's wife Lakshmee), and Gangaa (River).

There are five types of Vaayu (air) - Praan, Apaan, Vyaan, Samaan, and Udaan.

A Pentagon has five sides.

A Cube has six sides.

There are six Seasons in India in a year - Sharada Ritu, Vasanta Ritu (Spring), Greeshma Ritu (Summer), Varshaa Ritu (Rainy Season), Patjhara (Fall or Autumn), Sheet Ritu (Winter)

There are six types of food - Bhakshya (which is swallowed), Bhojya, Lehya (which is licked), Choshya (which is sucked)

There are six Chakra in a human body where six lotuses bloom, They are:

The seventh lotus, the white color lotus, is in the head of the human being, which has thousand petals and on that Lord Vishnu, the symbol of man's spiritual knowledge, sits.

There are seven Days in a week - Sunday, Monday, Tuesday, Wednesday, Thursday, Friday and Saturday.

There are seven Rishi (Saints), in the form of seven stars, near the Dhruv Taaraa (Polar Star). They revolve around it. They are different in every Kalp. One Kalp is about 71 plus 4-Yug period.

There are seven sacred Cities - (1) Ayodhyaa (UP), (2) Mathuraa (UP), (3) Haridwaar, (4) Kaashee (UP), (5) Kaanchee (Tamilnaadu), (6) Avantee or Ujjain (MP), and (7) Dwaarakaa (Gujaraat).

There are seven sacred Rivers - Gangaa, Yamunaa, Sindhu, Saraswatee, Godaavaree, Narmadaa, and Kaaveree.

There are eight Deviyaan, who are worshipped during Navraatri period:

(1)  Lakshamee Devee
(2)  Kaalee Devee
(3)  Saraswatee Devee
(4)  Sheetalaa Maataa
(5)  Paarvatee Jee, or Gauraa Devee
(6)  Durgaa Maataa
(7)  Hingalaaj
(8)  Bhuvaneshwaree

There are only eight elephants who are born in Devtaa Yoni - 

(1) Kumud
(2) Airaavat
(3) Padm
(4) Pushpdant
(5) Vaaman
(6) Suprateek
(7) Anjan
(8) Saarvbhaum 

There are nine Grah (Planets) - (1) Sun, (2) Moon, (3) Mars, (4) Mercury, (5) Jupiter, (6) Venus, (7) Saturn, (8) Raahu and (9) Ketu. Raahu and Ketu are not real planets but are only Shadow planets. These nine planets are imagined in human body too.

Sun lives in forehead
Moon lives just one finger below the Sun, in Bindu Chakra
Mars lives in eyes
Mercury lives in heart
Jupiter lives in navel in Manipoorak Chakra
Venus lives in semen
Saturn lives in navel
Rahu lives in mouth
Ketu lives in from heart to neck

There are nine Gems (Nava Ratn),  which are useful to wear in various Planets' periods. These nine Gems (Nav Ratn), govern the nine Planets (Nav Grah given above, traditionally accepted in Hindu astrology. These are --

Ruby (Laal) governing Sun,
Pearl (Motee) governing Moon,
Coral (Moongaa) governing Mars,
Emerald (Pannaa) governing Mercury,
Pukharaaj (Yellow Sapphire) governing Jupiter,
Diamond (Heeraa) governing Venus,
Blue Sapphire (Neelam) governing Saturn,
Hessonite governing Rahu and
Cat's Eye governing Ketu.

There were nine Gems (Nav Ratn) in Emperor Akbar the Great's court. Akbar ruled India from 1560 to 1605. Their names were:

(1) Birbal - the very witty Minister and personal advisor of Akbar. He
     has lots of his stories on his credit for everybody to laugh at and
     learning
(2) Taansen - the renowned musician of India. He used to light fire and
     bring rains through his singing
(3) Raajaa Todarmal - his financial wizard,
(4) Raajaa Maan Singh -  mighty general, famous for his chivalry,
(5) Abul Fazal - a great historian 
(6) Faizi - brother of Abul Fazal, a great poet 
(7) Daswant - a great painter
(8) Abdu us-Samad - a brilliant calligrapher and designer of Imperial coins
(9) Mir Fareh-ullah Shirazi - financier, philosopher, physician and
     astronomer

There were nine Gems (Nav Ratn) in King Vikramaaditya's court also

(1) Dhanvantari - enlightened the world upon the subjects of medicines and incantations.
(2) Kshapanak - treated the primary elements.
(3) Amar Singh - compiled a Sanskrit dictionary and a philosophical treatise.
(4) Shankubetaal Bhatt - compose comments, and Ghatakarpar - a poetical work.
(5) Mihir - his works are not mentioned.
(6) Varaah - produced works on astrology and Arithmetic.
(7) Vararuchi - introduced improvements in grammar, commented upon incantations and wrote a poem in praise of King Maadhav.
(8) Kaalidaas - wrote Sanskrit dramas - Shakuntalaa and Vikram and Urvashee, and many other books in Sanskrit

There are nine main Incarnations of Lord Vishnu. The tenth one is yet to come. See the details this in section for number TEN.