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A125297
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Number of nonempty subsets S of {1,2,3,...,n} such that each member of S divides the sum of all members of S.
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0
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1, 2, 4, 5, 6, 9, 10, 12, 15, 17, 18, 24, 25, 27, 31, 34, 35, 42, 43, 59, 62, 63, 64, 82, 83, 84, 88, 97
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| a(n) = a(n-1) + the number of subsets of S which meet the criteria that include the element n. - Robert G. Wilson v.
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MATHEMATICA
| (*first do*) Needs["Combinatorica`"] (*then*) f[n_] := f[n] = Block[{c = 0, k = 0, lmt = 2^(n - 1), lst = Range[n - 1], s = {}}, While[k < lmt + 1, k++; s = NextSubset[lst, s]; t = Join[s, {n}]; If[ Union[ IntegerQ@ # & /@ (Plus @@ t/t)] == {True}, c++ ]]; c]; Do[ Print[{n, f@n}], {n, 28}]; Table[ Sum[ f@i, {i, n}], {n, 28}] (* Robert G. Wilson v (rgwv(AT)rgwv.com), Jul 18 2007 *)
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CROSSREFS
| Sequence in context: A069470 A047435 A132791 * A194469 A143072 A089648
Adjacent sequences: A125294 A125295 A125296 * A125298 A125299 A125300
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KEYWORD
| nonn
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AUTHOR
| John W. Layman (layman(AT)math.vt.edu), Dec 08 2006
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