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Search: id:A065771
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| A065771 |
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Prime powers n such that both tau[n^2] and sigma[n^2] are composite numbers. |
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+0
2
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| 16, 81, 128, 625, 1024, 2187, 2401, 4096, 8192, 14641, 28561, 59049, 65536, 78125, 83521, 130321, 131072, 279841, 524288, 531441, 707281, 823543, 923521, 1594323, 1874161, 2825761, 3418801, 4194304, 4879681, 7890481, 9765625
(list; graph; listen)
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OFFSET
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1,1
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FORMULA
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A000005[A025475(n)^2] and A000203[A025475(n)^2] are composite numbers.
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MATHEMATICA
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Do[ s=DivisorSigma[ 0, n^2 ]; y=DivisorSigma[ 1, n^2 ]; If[ Equal[ Length[ FactorInteger[ n ] ], 1 ]&&!PrimeQ[ n ] &&!PrimeQ[ s ]&&!PrimeQ[ y ], Print[ n ] ], {n, 1, 10000000} ]
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CROSSREFS
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Cf. A000005, A000203, A065403-A065405, A028982, A025475
Sequence in context: A053167 A110892 A088040 this_sequence A041490 A096020 A016898
Adjacent sequences: A065768 A065769 A065770 this_sequence A065772 A065773 A065774
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KEYWORD
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nonn
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AUTHOR
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Labos E. (labos(AT)ana.sote.hu), Nov 19 2001
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