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A009205
a(n) = gcd(d(n), sigma(n)).
16
1, 1, 2, 1, 2, 4, 2, 1, 1, 2, 2, 2, 2, 4, 4, 1, 2, 3, 2, 6, 4, 4, 2, 4, 1, 2, 4, 2, 2, 8, 2, 3, 4, 2, 4, 1, 2, 4, 4, 2, 2, 8, 2, 6, 6, 4, 2, 2, 3, 3, 4, 2, 2, 8, 4, 8, 4, 2, 2, 12, 2, 4, 2, 1, 4, 8, 2, 6, 4, 8, 2, 3, 2, 2, 2, 2, 4, 8, 2, 2, 1, 2, 2, 4, 4, 4, 4, 4, 2, 6, 4, 6, 4, 4, 4, 12, 2, 3, 6, 1, 2, 8, 2, 2, 8, 2, 2, 4, 2, 8, 4, 2, 2, 8, 4, 6, 2, 4, 4, 8
OFFSET
1,3
LINKS
MATHEMATICA
Table[GCD[DivisorSigma[0, n], DivisorSigma[1, n]], {n, 120}] (* Harvey P. Dale, Dec 05 2017 *)
PROG
(PARI) A009205(n) = gcd(numdiv(n), sigma(n)); \\ Antti Karttunen, May 22 2017
(Python)
from math import prod, gcd
from sympy import factorint
def A009205(n):
f = factorint(n).items()
return gcd(prod(e+1 for p, e in f), prod((p**(e+1)-1)//(p-1) for p, e in f)) # Chai Wah Wu, Jul 27 2023
CROSSREFS
KEYWORD
nonn
EXTENSIONS
Data section extended to 120 terms by Antti Karttunen, May 22 2017
STATUS
approved