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 A319527 a(n) = 7 * sigma(n). 7
 7, 21, 28, 49, 42, 84, 56, 105, 91, 126, 84, 196, 98, 168, 168, 217, 126, 273, 140, 294, 224, 252, 168, 420, 217, 294, 280, 392, 210, 504, 224, 441, 336, 378, 336, 637, 266, 420, 392, 630, 294, 672, 308, 588, 546, 504, 336, 868, 399, 651, 504, 686, 378, 840, 504, 840, 560, 630, 420, 1176, 434, 672, 728, 889 (list; graph; refs; listen; history; text; internal format)
 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 step 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). a(n) = A000203(n) + A274536(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 k times sigma(n), k=1..8: A000203, A074400, A272027, A239050, A274535, A274536, this sequence, A319528. Cf. A216606, A237593. Sequence in context: A063469 A155131 A160890 * A297178 A325553 A032639 Adjacent sequences:  A319524 A319525 A319526 * A319528 A319529 A319530 KEYWORD nonn,easy AUTHOR Omar E. Pol, Sep 22 2018 STATUS approved

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Last modified June 6 04:11 EDT 2020. Contains 334858 sequences. (Running on oeis4.)