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A160994
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Least prime power having n divisors such that every sum of two or more divisors is composite.
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0
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3, 7, 7, 19, 19, 139, 151, 211, 211, 211, 421, 2311, 2311, 92401, 120121, 120121, 180181, 2312311
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OFFSET
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2,1
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LINKS
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Table of n, a(n) for n=2..19.
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MATHEMATICA
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(* first do *) Needs["Combinatorica`"] (* then *) f[n_] := Block[{d = Divisors@n, k, mx}, k = 1 + Length@d; mx = 2^Length[d]; While[k < mx && !PrimeQ[Plus @@ NthSubset[k, d]], k++ ]; If[k == mx, Length@d, 0]];
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CROSSREFS
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Sequence in context: A239047 A229521 A263337 * A113833 A212286 A157102
Adjacent sequences: A160991 A160992 A160993 * A160995 A160996 A160997
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KEYWORD
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nonn
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AUTHOR
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Robert G. Wilson v, Jun 01 2009
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STATUS
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approved
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