A063944 Final nonzero digit of (n!)! (A000197).

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, 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, 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

Offset

0,3

Links

David W. Wilson, Table of n, a(n) for n = 0..10000

Index entries for sequences related to final digits of numbers

Prog

(PARI) for(n=0, 22, m=n!!; while(Mod(m, 10) == 0, m=m/10); print(Mod(m, 10)))
(Python)
from functools import reduce
from math import prod, factorial
from sympy.ntheory.factor_ import digits
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

Crossrefs

Cf. A000197, A008904.

Sequence in context: A368745 A185421 A219976 * A086447 A324032 A196872

Adjacent sequences: A063941 A063942 A063943 * A063945 A063946 A063947

Keyword

nonn,base

Author

Jason Earls, Sep 01 2001

Extensions

More terms from David W. Wilson, Sep 05 2001, who remarks that "I'll tell you, computing (107!)! took up some disk space!"

Status

approved