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A072607
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If D[n] is divisor-set of n, then in set of 1+D only 2 primes occur:{2,3}; also n is not squarefree.
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0
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98, 338, 578, 686, 722, 1274, 1862, 1922, 2366, 2738, 3038, 3626, 3698, 4214, 4394, 4418, 4802, 5054, 5978, 6422, 6566, 6962, 7154, 7442, 7742, 8918, 8978, 9386, 9506, 9826, 9898, 10082, 10094, 10478, 10658, 10682, 12446, 12482, 12506, 13034, 13426
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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EXAMPLE
| n=338=2.13.13 is not squarefree; D={1,2,13,26,169,338};1+D={2,3,14,27,170,339} contains only two primes {2,3}. Such numbers are non-squarefree even non-totient numbers (from A005277), present also in A051222. Their odd prime-divisors seem to arise from A053176.
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MATHEMATICA
| di[x_] := Divisors[x] dp[x_] := Part[di[x], Flatten[Position[PrimeQ[1+di[x]], True]]]+1 Do[s=Length[dp[n]]; If[Equal[s, 2]&&Equal[MoebiusMu[n], 0], Print[n]], {n, 1, 25000}]
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CROSSREFS
| Cf. A000005, A005277, A002202, A067513, A051222, A053176.
Sequence in context: A202378 A202371 A195751 * A160828 A158129 A071319
Adjacent sequences: A072604 A072605 A072606 * A072608 A072609 A072610
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KEYWORD
| nonn
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Jun 24 2002
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