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A070763
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Numbers n such that sigma(n) is a power of prime (of the form p^a, p prime, a>=1).
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2
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2, 3, 4, 7, 9, 16, 21, 25, 31, 64, 81, 93, 127, 217, 289, 381, 400, 651, 729, 889, 1681, 2401, 2667, 3481, 3937, 4096, 5041, 7921, 8191, 10201, 11811, 15625, 17161, 24573, 27559, 27889, 28561, 29929, 57337, 65536, 82677, 83521, 85849
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OFFSET
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1,1
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COMMENTS
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LINKS
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EXAMPLE
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sigma(57337)=2^16 hence 57337 is in the sequence.
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MATHEMATICA
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Select[Range[100000], PrimePowerQ[DivisorSigma[1, #]] &] (* Ivan Neretin, Feb 08 2017 *)
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PROG
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(PARI) for(n=1, 100000, if(omega(sigma(n)) == 1, print1(n, ", ")))
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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