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A274535
a(n) = 5*sigma(n).
16
5, 15, 20, 35, 30, 60, 40, 75, 65, 90, 60, 140, 70, 120, 120, 155, 90, 195, 100, 210, 160, 180, 120, 300, 155, 210, 200, 280, 150, 360, 160, 315, 240, 270, 240, 455, 190, 300, 280, 450, 210, 480, 220, 420, 390, 360, 240, 620, 285, 465, 360, 490, 270, 600, 360, 600, 400, 450, 300, 840, 310, 480, 520, 635
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).
FORMULA
a(n) = 5*A000203(n) = A000203(n) + A239050(n) = A074400(n) + A272027(n).
Dirichlet g.f.: 5*zeta(s-1)*zeta(s). - Ilya Gutkovskiy, Jul 04 2016
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
k times sigma(n), k=1..6: A000203, A074400, A272027, A239050, this sequence, A274536.
Cf. A237593.
Sequence in context: A273908 A271576 A345645 * A027184 A328249 A110702
KEYWORD
nonn,easy
AUTHOR
Omar E. Pol, Jun 29 2016
STATUS
approved