OFFSET
1,1
COMMENTS
7 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 (360/7)-degree-three-dimensional sector arises after the (360/7)-degree-zig-zag folding of every row of the diagram of the isosceles triangle A237593. The top of the pyramid is a seven-pointed star formed by seven rhombuses (see Links section).
LINKS
FORMULA
a(n) = 7*A000203(n).
Dirichlet g.f.: 7*zeta(s-1)*zeta(s). - (After Ilya Gutkovskiy)
MAPLE
with(numtheory): seq(7*sigma(n), n=1..64);
MATHEMATICA
7*DivisorSigma[1, Range[70]] (* Harvey P. Dale, Mar 14 2020 *)
PROG
(PARI) a(n) = 7 * sigma(n);
(GAP) List([1..70], n->7*Sigma(n)); # Muniru A Asiru, Sep 28 2018
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Omar E. Pol, Sep 22 2018
STATUS
approved