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%I #27 Dec 07 2023 11:40:22
%S 1,1,2,2,6,6,6,4,6,8,2,8,8,6,4,4,6,6,8,2,6,4,4,8,2,2,6,2,2,6,4,6,2,2,
%T 8,4,6,8,2,2,2,2,8,6,6,6,2,2,6,8,4,2,2,2,8,8,4,4,2,6,8,6,4,6,6,4,8,2,
%U 2,4,4,2,8,2,8,2,4,2,8,8,6,8,2,8,4,4,6,8,8,6,2,4,6,2,6,4,2,6,4,6,2,6,4,2,8,2,4,2
%N Final nonzero digit of (n!)! (A000197).
%H David W. Wilson, <a href="/A063944/b063944.txt">Table of n, a(n) for n = 0..10000</a>
%H <a href="/index/Fi#final">Index entries for sequences related to final digits of numbers</a>
%o (PARI) for(n=0,22,m=n!!; while(Mod(m,10) == 0,m=m/10); print(Mod(m,10)))
%o (Python)
%o from functools import reduce
%o from math import prod, factorial
%o from sympy.ntheory.factor_ import digits
%o def A063944(n): return reduce(lambda x,y:x*y%10,((1,1,2,6,4)[a]*((6,2,4,8)[i*a&3] if i*a else 1) for i, a in enumerate(digits(factorial(n),5)[-1:0:-1])))*6%10 if n>1 else 1 # _Chai Wah Wu_, Dec 07 2023
%Y Cf. A000197, A008904.
%K nonn,base
%O 0,3
%A _Jason Earls_, Sep 01 2001
%E More terms from _David W. Wilson_, Sep 05 2001, who remarks that "I'll tell you, computing (107!)! took up some disk space!"