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A080666
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Numbers k such that k^2 + 1 and k^2 - 1 are not squarefree.
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1
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7, 41, 43, 57, 82, 93, 99, 107, 117, 118, 143, 157, 168, 193, 207, 239, 243, 251, 257, 293, 307, 327, 332, 343, 357, 368, 393, 407, 437, 443, 457, 493, 507, 515, 532, 540, 543, 557, 568, 577, 593, 606, 607, 643, 657, 693, 707, 743, 746, 757, 775, 776, 782
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OFFSET
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1,1
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COMMENTS
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This sequence is infinite. For instance, it contains all numbers of the form 100*m + 7. - Emmanuel Vantieghem, Oct 25 2016
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LINKS
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MATHEMATICA
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Select[Range[10^3], ! SquareFreeQ[ #^2 - 1] && ! SquareFreeQ[ #^2 + 1] &]
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PROG
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(Magma) [n : n in [2..800] | not IsSquarefree(n^2-1) and not IsSquarefree(n^2+1)]; // Vincenzo Librandi, Oct 26 2016
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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