OFFSET
1,1
COMMENTS
6 times the sum of the divisors of n.
a(n) is also the total number of horizontal rhombuses in the terraces of the n-th level of an irregular stepped pyramid (starting from the top) in which the structure of every 60-degree-three-dimensional sector arises after the 60-degree-zig-zag folding of every row of the diagram of the isosceles triangle A237593. The top of the pyramid is a six-pointed star formed by six rhombuses (see Links section).
LINKS
FORMULA
Dirichlet g.f.: 6*zeta(s-1)*zeta(s). - Ilya Gutkovskiy, Jul 04 2016
Conjecture: a(n) = sigma(5*n) = A283118(n) iff n is not a multiple of 5. - Omar E. Pol, Oct 02 2018
MAPLE
with(numtheory): seq(6*sigma(n), n=1..64);
MATHEMATICA
6DivisorSigma[1, Range[50]] (* Alonso del Arte, Jul 04 2016 *)
PROG
(PARI) a(n) = 6 * sigma(n);
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Omar E. Pol, Jun 29 2016
STATUS
approved