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A326122
a(n) = 10 * sigma(n).
2
10, 30, 40, 70, 60, 120, 80, 150, 130, 180, 120, 280, 140, 240, 240, 310, 180, 390, 200, 420, 320, 360, 240, 600, 310, 420, 400, 560, 300, 720, 320, 630, 480, 540, 480, 910, 380, 600, 560, 900, 420, 960, 440, 840, 780, 720, 480, 1240, 570, 930, 720, 980, 540, 1200, 720, 1200, 800, 900, 600, 1680, 620, 960
OFFSET
1,1
COMMENTS
10 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) where the structure of every 36-degree-three-dimensional sector arises after the 36-degree-zig-zag folding of every row of the diagram of the isosceles triangle A237593. The top of the pyramid is a 10-pointed star formed by 10 rhombuses (see Links section).
FORMULA
a(n) = 10*A000203(n) = 5*A074400(n) = 2*A274535(n).
a(n) = A000203(n) + A325299(n) = A074400(n) + A319528(n).
Dirichlet g.f.: 10*zeta(s-1)*zeta(s). - (After Ilya Gutkovskiy)
MAPLE
with(numtheory): seq(10*sigma(n), n=1..64);
MATHEMATICA
10*DivisorSigma[1, Range[70]] (* After Harvey P. Dale *)
PROG
(PARI) a(n) = 10 * sigma(n);
(GAP) List([1..70], n->10*Sigma(n)); # After Muniru A Asiru
(Magma) [10*DivisorSigma(1, n): n in [1..70]]; // Vincenzo Librandi, Jul 26 2019
KEYWORD
nonn,easy
AUTHOR
Omar E. Pol, Jul 13 2019
STATUS
approved