

A089653


Numbers k > 1 such that (product of prime factors of k)  1 is a perfect square.


5



2, 4, 5, 8, 10, 16, 17, 20, 25, 26, 32, 37, 40, 50, 52, 64, 65, 80, 82, 100, 101, 104, 122, 125, 128, 145, 160, 164, 170, 197, 200, 208, 226, 244, 250, 256, 257, 289, 290, 320, 325, 328, 338, 340, 362, 400, 401, 416, 442, 452, 485, 488, 500, 512, 530, 577, 580
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OFFSET

1,1


LINKS



EXAMPLE

The prime factors of 10 are 2 and 5 and 2 * 5  1 = 9 is a square; so 10 belongs to the sequence.


MATHEMATICA

ppf[n_] := Apply[Times, Transpose[FactorInteger[n]][[1]]]; Select[Range[2, 10^3], IntegerQ[Sqrt[ppf[ # ]  1]] &]


PROG

(PARI) isok(k) = (k>1) && issquare(vecprod(factor(k)[, 1])1); \\ Michel Marcus, Sep 05 2023


CROSSREFS



KEYWORD

nonn


AUTHOR



EXTENSIONS



STATUS

approved



