OFFSET
1,1
COMMENTS
5 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 72-degree-three-dimensional sector arises after the 72-degree-zig-zag folding of every row of the diagram of the isosceles triangle A237593. The top of the pyramid is a five-pointed star formed by five rhombuses (see Links section).
LINKS
FORMULA
MAPLE
with(numtheory): seq(5*sigma(n), n=1..64);
MATHEMATICA
Table[5 DivisorSigma[1, n], {n, 64}] (* Michael De Vlieger, Jul 04 2016 *)
PROG
(PARI) a(n) = 5 * sigma(n);
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Omar E. Pol, Jun 29 2016
STATUS
approved