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 A060872 Sum of d*d' over all unordered pairs (d,d') with d*d' = n. 4
 1, 2, 3, 8, 5, 12, 7, 16, 18, 20, 11, 36, 13, 28, 30, 48, 17, 54, 19, 60, 42, 44, 23, 96, 50, 52, 54, 84, 29, 120, 31, 96, 66, 68, 70, 180, 37, 76, 78, 160, 41, 168, 43, 132, 135, 92, 47, 240, 98, 150, 102, 156, 53, 216, 110, 224, 114, 116, 59, 360, 61, 124, 189, 256 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..5000 FORMULA a(n) = n * ceiling( d(n)/2) where d is the number of divisors function. G.f.: x*f'(x), where f(x) = Sum_{k>=1} x^k^2/(1 - x^k). - Ilya Gutkovskiy, Apr 10 2017 EXAMPLE a(4)=8 because pairs of factors are 1*4 and 2*2 and 1*4 + 2*2 = 8. MATHEMATICA Table[ n * Ceiling[ DivisorSigma[0, n] /2 ], {n, 1, 73} ] PROG (MAGMA) [n*Ceiling(DivisorSigma(0, n)/2): n in [1..70]]; // Vincenzo Librandi, Apr 12 2017 CROSSREFS Cf. A060866. First differences of A083356. Sequence in context: A011433 A126139 A296070 * A162775 A066959 A086471 Adjacent sequences:  A060869 A060870 A060871 * A060873 A060874 A060875 KEYWORD nonn,easy AUTHOR N. J. A. Sloane, May 04 2001 EXTENSIONS More terms from Robert G. Wilson v, Jun 23 2001 STATUS approved

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Last modified January 18 06:34 EST 2019. Contains 319269 sequences. (Running on oeis4.)