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A063944
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Final nonzero digit of (n!)! (A000197).
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2
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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
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OFFSET
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0,3
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LINKS
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PROG
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(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
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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More terms from David W. Wilson, Sep 05 2001, who remarks that "I'll tell you, computing (107!)! took up some disk space!"
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STATUS
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approved
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