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 A065771 Prime powers n such that both tau(n^2) and sigma(n^2) are composite numbers. 2
 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, 12117361, 13845841, 16777216 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Donovan Johnson, Table of n, a(n) for n = 1..1000 FORMULA A000005(A025475(n)^2) and A000203(A025475(n)^2) are composite numbers. MATHEMATICA 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} ] CROSSREFS Cf. A000005, A000203, A065403-A065405, A028982, A025475. Sequence in context: A110892 A202880 A088040 * A320965 A295071 A223951 Adjacent sequences:  A065768 A065769 A065770 * A065772 A065773 A065774 KEYWORD nonn AUTHOR Labos Elemer, Nov 19 2001 STATUS approved

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Last modified May 28 21:37 EDT 2020. Contains 334690 sequences. (Running on oeis4.)