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 A168654 The sum of the proper divisors of n, weighted by divisor multiplicity, equals n. 0
 6, 152, 656, 2888, 18632, 36224, 55328384, 1082574464 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The multiplicity of a divisor d > 1 in n is defined as the largest power i for which d^i divides n; otherwise is defined as 1 if d = 1. From Ray Chandler, Dec 08 2009: (Start) Also in the sequence, but not necessarily the next terms, 2^k * p where p = A168512(2^k) is prime: 2^18 * 525529 = 137764274176, 2^25 * 67117859 = 2252101635801088, 2^26 * 134234921 = 9008353057439744, 2^30 * 2147551801 = 2305916187940225024, 2^40 * 2199025372073 = 2417853966368708281499648, 2^50 * 2251799880936649 = 2535301276174804923929356926976, as well as k = 150, 348, 694, ... (End) LINKS EXAMPLE The proper divisors of 152 are 1, 2, 4, 8, 19, 38, 76 of multiplicity 1, 3, 1, 1, 1, 1, 1 respectively. Since 1*1 + 3*2 + 1*4 + 1* 8 + 1*19 + 1*38 + 1*76 = 152, then 152 belongs to the sequence. MATHEMATICA (*multiplicity of d in n*) divmult[d_, n_] := Module[{output, i}, If[d == 1, output = 1, If[d == n, output = 1, i = 0; While[Mod[n, d^(i + 1)] == 0, i = i + 1]; output = i]]; output]; (*sum of divisors weighted by divisor multiplicity*) dmt[n_] := Module[{divs, l}, divs = Divisors[n]; l = Length[divs]; Sum[divmult[divs[[i]], n]*divs[[i]], {i, 1, l}]]; (*search for sequence terms*) ls = {}; Do[If[dmt[n] == 2 n, ls = Append[ls, n]], {n, 2, 10^7}]; ls CROSSREFS Cf. A168512 Sequence in context: A165436 A261066 A297737 * A147796 A003766 A278728 Adjacent sequences:  A168651 A168652 A168653 * A168655 A168656 A168657 KEYWORD more,nonn AUTHOR Joseph L. Pe, Dec 01 2009 EXTENSIONS a(7)-a(8) from Ray Chandler, Dec 08 2009 STATUS approved

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Last modified October 23 20:17 EDT 2019. Contains 328373 sequences. (Running on oeis4.)