OFFSET
1,2
COMMENTS
Most (not all) of the terms are of the form:
x^2-y^2, for x>y>0.
31=16^2-15^2,
64=10^2-6^2=17^2-15^2,
79=40^2-39^2,
91=10^2-3^2=46^2-45^2,
111=20^2-17^2=56^2-55^2,
148=11^2-3^3=38^2-36^2,
151=76^2-75^2,
205=23^2-18^2=103^2-102^2,
211=106^2-105^2.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..62
EXAMPLE
2^22-2=2*7^2*127*337, 2^22+2=2*3^2*43*5419.
MATHEMATICA
Select[Range@211, !(SquareFreeQ[2^#-2]||SquareFreeQ[2^#+2])&]
PROG
(PARI) isok(n) = !issquarefree(2^n-2) && !issquarefree(2^n+2); \\ Michel Marcus, Oct 04 2019
CROSSREFS
KEYWORD
nonn,hard
AUTHOR
Vladimir Joseph Stephan Orlovsky, Mar 22 2011
EXTENSIONS
a(14)-a(30) from D. S. McNeil, Mar 23 2011
a(31)-a(54) from Amiram Eldar, Oct 04 2019
STATUS
approved