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%I #33 Sep 17 2018 03:37:16
%S 0,1,3,15,79,511,4095,6735,65535,2097151,16777215,75955411,
%T 68719476735,137438953471
%N Numbers k such that k^2 + 1 divides 2^k + 2.
%C Numbers t such that 2^t-1 is a term are 0, 1, 2, 4, 9, 12, 16, 21, ...
%C Primes p such that 2^((p^2-1)/2)-1 is a term are 3, 5, 7, 13, 19, 29, 37, 43, 47, 61, 71, 89, 103, 107, 127, 131, 139, 173, 191, 211, ...(cf. A062326).
%C a(14) > 10^11. - _Hiroaki Yamanouchi_, Sep 14 2018
%o (PARI) isok(n)=Mod(2, n^2+1)^n==-2;
%Y Cf. A015921, A062326, A097958, A244673, A247220.
%K nonn,more
%O 1,3
%A _Altug Alkan_, Sep 13 2018, following a suggestion from _Max Alekseyev_
%E a(13) from _Hiroaki Yamanouchi_, Sep 14 2018
%E a(14) from _Giovanni Resta_, Sep 17 2018
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