Satoshi sets total number of bitcoins to 21 million at line 680 of "main.cpp" file mathematically. above this line there is a comment writted by satoshi: "Subsidy is cut in half every 4 years" link:
https://github.com/Maguines/Bitcoin-v0.1/blob/master/bitcoin0.1/src/main.cpp. if the question be about total number of bitcoins this comment is the answer. if we convert "4" to "four" the result has 32 character and 8 words!
you mistunderstood the whole thing here! most probably because you Ctrl+F searched the number "21" and found that line. which is not even 21 million but 210 thousand.
that line which you posted is not the 21 million limit although it is somewhat related. what is happening there is that every 210000 (210k) blocks we cut the block reward by half. an event known as Halvening these days! and 4 years is the result of time between blocks thanks to difficulty (210000 ~= 4 * 365 * 24 * 6 block/h)
AFAIK nowhere in the source code there is any constant set for maximum number of bitcoins. it just happens to be that much because of the way all these other things are calculated (block reward, block reward halving,...)
No! I don't misunderstood. I did not say that number is 21 million. if you read my replay carefully, I said satoshi calculated total number of bitcoins MATHEMATICALLY. in fact the total number of bitcoins is not in source code as a constant number. number of bitcoins was generated in first block is 50, this act repeats every 10 minute. that line of code halve the generated bitcoins every 4 years, this means number of generated bitcoins some day will be 0. it will takes 140 years to number of generated bitcoins become 0. if we sum all generated bitcoins in 140 years this number becomes about 21 million. if this HALVING does not take place the number of generated bitcoins will be infinite.