They asked a Ultimate Question of Life, the Universe and Everything to Deep Thought. Deep Thought replied that: 42
If we need to attribute a meaning to number of 42 binary code system comes first cause the machine gives the answer of Ultimate Question of Life, the Universe and Everything. In a binary code system 42 correspond to 101010 that means exist- nonexist- exist- nonexist- exist- nonexist.
42 means “4 (for) and 2 (to) in separatedly. For moving forward you have to give back. If we divide 42 in 2 equal parts. 21 means “to only one” and 1 refers to ourselves. 2 refers to society.
If we multiply 4 and 2 we get 8. 8 seems like infinity. So life give infinite opportunity for us
And there is also different meaning in different religions
Hinduism/ Sanatana Dharma: Universe is formed of two halves: Shiva and Shakti. They together denote “Creation”, “Life” which is the most peculiar quality of our universe. It is what keeps Universe going on and on for billions of years, be it any species.
Shiva (has 12 Jyotirlingas) + Shakti (9 forms) = “21”
Islam: Its very straight forward here because of the divine number 786. Some believe it to be a representation of Sanskrit Om, which is the divine vibration which created universe. 7 + 8 + 6 = “21”.
Christianity: The Holy Trinity which is also present in Hinduism too as in Brahma-Vishnu-Mahesh, it gives “3” (2+1).
(Chandra, 2016)
The answer to this is very simple,” Adams said. “It was a joke. It had to be a number, an ordinary, smallish number, and I chose that one. Binary representations, base 13, Tibetan monks are all complete nonsense. I sat on my desk, stared in to the garden and thought 42 will do. I typed it out. End of story.
THE HITCHHIKER'S GUIDE TO THE GALAXY 