OFFSET
1,4
COMMENTS
a(n) = A001157(n) - n^2.
a(n) = 1 if and only if n is prime.
LINKS
T. D. Noe, Table of n, a(n) for n=1..10000
FORMULA
Dirichlet g.f.: zeta(s-2)*(zeta(s) - 1). - Ilya Gutkovskiy, Sep 08 2016
EXAMPLE
a(12) = 1^2 + 2^2 + 3^2 + 4^2 + 6^2 = 1 + 4 + 9 + 16 + 36 = 66.
MATHEMATICA
Table[DivisorSigma[2, n] - n^2, {n, 1, 64}] (* Jean-François Alcover, Mar 01 2019 *)
PROG
(PARI) a(n)=sigma(n, 2)-n^2 \\ Charles R Greathouse IV, Dec 07 2011
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jan 29 2002
STATUS
approved