OFFSET
1,2
COMMENTS
Is this sequence infinite?
Are there other prime terms except a(4) = 601021?
Let f(n) be the smallest k > 1 such that k^2 + n divides 2^k - 2. f(0) = 1093 (cf. A001220), f(1) = 95 and f(2) = a(2) = 166751.
The next term, if it exists, is > 10^9. - Vaclav Kotesovec, Oct 23 2018
a(7) > 1.9*10^11, if it exists. - Giovanni Resta, Oct 29 2018
MATHEMATICA
Select[Range[10^7], IntegerQ[(2^# - 2) / (#^2 + 2)] &] (* Vincenzo Librandi, Sep 21 2018 *)
PROG
(PARI) isok(n) = Mod(2, n^2+2)^n==2;
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Altug Alkan, Sep 16 2018
STATUS
approved