

Why does factorial(21) equal -4249290049419214848? - adambom
http://www.johnmyleswhite.com/notebook/2013/01/03/computers-are-machines/

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MaysonL
Factorial, not fib

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gordaco
Although fib grows exponentially, so it does the same for not so big numbers
(a back-of-an-envelope calculation gives me that fib(91) doesn't fit in 63
bits).

OTOH, if I had to calculate fib(X), and not fib(1..X), I'd use the exponential
formula (relying on floating point) instead of the recurrence (which uses
integer), so I guess the error would be detected at the conversion to integer.

