Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #8 Sep 23 2018 20:57:17
%S 1,1,9,1,1,1,1,1,27,25,1,1,1,1,9,1,1,1,1,1,9,1,1,1,1,1,81,1,1,25,1,1,
%T 9,1,1,1,1,1,9,1,1,1,1,1,27,1,1,1,1,125,9,1,1,1,121,1,9,1,1,1,1,1,27,
%U 1,1,1,1,289,9,25,1,1,1,1,9,1,1,169,1,1,243,1,1,1,1,1,9,1,1,25,1,1,9,1,1,1
%N a(n) = gcd(1 + 2^n, n^2).
%H Antti Karttunen, <a href="/A087968/b087968.txt">Table of n, a(n) for n = 1..65537</a>
%e a(9) = gcd(2^9 + 1,9^2) = gcd(513,81) = 27.
%p seq(gcd(2^n+1,n^2),n=1..100); # _Muniru A Asiru_, Sep 22 2018
%o (PARI) A087968(n) = gcd((2^n)+1, n^2); \\ _Antti Karttunen_, Sep 22 2018
%o (GAP) List([1..100],n->Gcd(2^n+1,n^2)); # _Muniru A Asiru_, Sep 22 2018
%Y Cf. A087966, A087969.
%K nonn
%O 1,3
%A _Labos Elemer_, Sep 22 2003