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

Offset

1,1

Links

Table of n, a(n) for n=1..16.

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

Cf. A005117, A013929, A184966, A184967, A188047.

Sequence in context: A043861 A043870 A296865 * A098159 A241847 A295487

Adjacent sequences: A188046 A188047 A188048 * A188050 A188051 A188052

Keyword

nonn,hard,more

Author

Vladimir Joseph Stephan Orlovsky, Mar 19 2011

Extensions

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

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

Status

approved