A188049 - OEIS

A188049

Numbers k such that k^k-1 and k^k+1 are both not squarefree.

17, 18, 19, 40, 49, 51, 53, 55, 69, 82, 89, 91, 97, 99, 117, 118

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OFFSET

1,1

LINKS

EXAMPLE

17 is a term since 17^17-1 = 2^4*10949*1749233*2699538733 and 17^17+1 = 2*3^2*45957792327018709121.

MATHEMATICA

Select[Range@41, !(SquareFreeQ[#^#-1]||SquareFreeQ[#^#+1])&]

PROG

(PARI) isok(k) = ! issquarefree(k^k-1) && ! issquarefree(k^k+1); \\ Michel Marcus, Feb 22 2021

CROSSREFS

KEYWORD

nonn,hard,more

AUTHOR

EXTENSIONS

a(5)-a(14) from D. S. McNeil, Mar 22 2011

a(15)-a(16) from Amiram Eldar, Feb 22 2021

STATUS

approved