%I #11 Feb 05 2022 19:36:53
%S 1681,3146,5917,308950,10553441,10553550,4273262954,9781980985
%N Numbers n with property that n*prime(n)+(n+1)*prime(n+1) is a perfect square s^2.
%C Or, numbers n with property that A033286(n)+A033286(n+1) is a perfect square s^2, A033286(n)=n*(n-th prime). [From _Zak Seidov_, Oct 12 2010]
%C a(9) > pi(4*10^12). [From _Donovan Johnson_, Oct 22 2010]
%e {n,s}: {1681,6943},{3146,13487},{5917,26299},{308950,1647737}, {10553441,63320647},{10553550,63321299}; no more n's up to 2*10^8.
%t Position[Total/@Partition[Table[n Prime[n],{n,310000}],2,1],_? (IntegerQ[ Sqrt[#]]&)]//Flatten (* The program generates the first four terms of the sequence. To generate more, Increase the Range constant, but the program may take a long time to run. *) (* _Harvey P. Dale_, Feb 05 2022 *)
%o (PARI) isok(n) = issquare(n*prime(n)+(n+1)*prime(n+1)); \\ _Michel Marcus_, Oct 19 2013
%K more,nonn
%O 1,1
%A _Zak Seidov_, Oct 11 2010
%E a(7)-a(8) from _Donovan Johnson_, Oct 22 2010