A301861 a(n) is the sum of the decimal digits of (n!)!.
1, 1, 2, 9, 81, 783, 7164, 69048, 711009, 7961040, 95935761, 1242436185, 17235507996
Offset: 0
Examples
a(0) = digitsum((0!)!) = digitsum(1!) = digitsum(1) = 1. a(1) = digitsum((1!)!) = digitsum(1!) = digitsum(1) = 1. a(2) = digitsum((2!)!) = digitsum(2!) = digitsum(2) = 2. a(3) = digitsum((3!)!) = digitsum(6!) = digitsum(720) = 7+2 = 9. a(4) = digitsum((4!)!) = digitsum(24!) = digitsum(620448401733239439360000) = 6+2+0+4+4+8+4+0+1+7+3+3+2+3+9+4+3+9+3+6+0+0+0+0 = 81.
Crossrefs
Programs
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Magma
[&+Intseq(Factorial(Factorial(n))): n in [0..10]]; // Vincenzo Librandi, Mar 29 2018
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Maple
a:= n-> add(i, i=convert(n!!, base, 10)): seq(a(n), n=0..8); # Alois P. Heinz, Oct 27 2021
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Mathematica
Table[Plus@@IntegerDigits[(n!)!], {n, 0, 10}] (* Vincenzo Librandi, Mar 29 2018 *) -
PARI
a(n) = sumdigits(n!!); \\ Michel Marcus, Mar 28 2018
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Python
from math import factorial def A301861(n): return sum(int(d) for d in str(factorial(factorial(n)))) # Chai Wah Wu, Mar 31 2018 # faster program for larger values of n from gmpy2 import mpz, digits, fac def A301861(n): return int(sum(mpz(d) for d in digits(fac(fac(n))))) # Chai Wah Wu, Oct 24 2021
Formula
Extensions
a(11) from Chai Wah Wu, Mar 31 2018
a(12) from Chai Wah Wu, Apr 01 2018
Comments