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A160994 Least prime power having n divisors such that every sum of two or more divisors is composite. 0
3, 7, 7, 19, 19, 139, 151, 211, 211, 211, 421, 2311, 2311, 92401, 120121, 120121, 180181, 2312311 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

LINKS

Table of n, a(n) for n=2..19.

MATHEMATICA

(* 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]];

CROSSREFS

Sequence in context: A239047 A229521 A263337 * A113833 A212286 A157102

Adjacent sequences:  A160991 A160992 A160993 * A160995 A160996 A160997

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Jun 01 2009

STATUS

approved

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Last modified September 16 12:41 EDT 2019. Contains 327113 sequences. (Running on oeis4.)