

A072607


If D[n] is divisorset of n, then in set of 1+D only 2 primes occur:{2,3}; also n is not squarefree.


1



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
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OFFSET

1,1


LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000


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 nonsquarefree even nontotient numbers (from A005277), present also in A051222. Their odd prime divisors seem to arise from A053176.


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}]


CROSSREFS

Cf. A000005, A005277, A002202, A067513, A051222, A053176.
Sequence in context: A202378 A202371 A195751 * A306214 A160828 A158129
Adjacent sequences: A072604 A072605 A072606 * A072608 A072609 A072610


KEYWORD

nonn


AUTHOR

Labos Elemer, Jun 24 2002


STATUS

approved



