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A036907
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Square refactorable numbers.
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4
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1, 9, 36, 225, 441, 625, 1089, 1521, 2025, 2601, 3249, 3600, 4761, 5625, 6561, 7569, 8100, 8649, 10000, 12321, 15129, 16641, 19881, 22500, 25281, 26244, 28224, 31329, 32400, 33489, 35721, 40401, 45369, 47961, 50625, 56169, 62001, 71289, 84681
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OFFSET
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1,2
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LINKS
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EXAMPLE
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9 is refactorable because tau(9)=3 and 3 divides 9 and 9 is a square number.
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MATHEMATICA
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Select[Range[300]^2, Divisible[#, DivisorSigma[0, #]]&] (* Harvey P. Dale, Nov 21 2020 *)
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PROG
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(PARI) isok(n) = issquare(n) && ! (n % numdiv(n)); \\ Michel Marcus, Aug 31 2013
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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Simon Colton (simonco(AT)cs.york.ac.uk)
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STATUS
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approved
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