OFFSET
1,4
COMMENTS
Number of even divisors of n minus number of odd strong divisors of n (i.e. odd divisors > 1).
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..65537
FORMULA
MATHEMATICA
nmax = 80; CoefficientList[Series[Sum[x^(2 k)/(1 + x^k), {k, 1, nmax}], {x, 0, nmax}], x] // Rest
Table[DivisorSum[n, (-1)^# &, # > 1 &], {n, 1, 80}]
PROG
(PARI) A325939(n) = sumdiv(n, d, if(1==d, 0, ((-1)^d))); \\ Antti Karttunen, Sep 20 2019
CROSSREFS
KEYWORD
sign,look
AUTHOR
Ilya Gutkovskiy, Sep 09 2019
STATUS
approved