Gamma function

[jack]

For 100!, the function from, "Numerical Recipes in C", is only correct for 9 digits, so the Lanczos implementation beats it.

Dan, both are Lanczos approximations, the one I posted uses more terms, but there's something wrong with thinBasic,
it's supposed to use extended precision in it's calculations but

Val("1e+4932")

gives

1.7014118346046923E+38