%I A104240
%S A104240 0,0,7,144,504,9727,187560,654840,12626287,243453384,849982464,
%T A104240 16388911447,316002305520,1103276584080,21272794432567,410170749112224
%N A104240 Nonnegative integers n such that 13*n^2 + 13*n + 1 is a square.
%C A104240 The next terms appear to be 243453384, 849982464, 16388911447.
%F A104240 a(1)=0, a(2)=0, a(3)=7, a(4)=144, a(5)=504, a(6)=9727 and then a(n)=1298*a(n-3)+648-a(n-6), 
               13*(a(n)^2)+13*a(n)+1 = a square. - Pierre CAMI (pierrecami(AT)tele2.fr), 
               Apr 05 2005
%o A104240 (PARI) for(n=0,12626287,if(issquare(13*n*(n+1)+1),print1(n,",")))
%Y A104240 Sequence in context: A070074 A051397 A082157 this_sequence A156978 A163028 
               A012826
%Y A104240 Adjacent sequences: A104237 A104238 A104239 this_sequence A104241 A104242 
               A104243
%K A104240 nonn
%O A104240 0,3
%A A104240 Gerald McGarvey (Gerald.McGarvey(AT)comcast.net), Apr 02 2005
%E A104240 More terms from Pierre CAMI (pierrecami(AT)tele2.fr), Apr 05 2005