cp's OEIS Frontend

A259256 With a(1) = 1, a(n) is the smallest number not already in the sequence such that a(n) + Product_{i=1..n-1} a(i) is a square.

%I A259256 #8 Jun 22 2015 19:05:14
%S A259256 1,3,6,7,18,36,148,5625,351225,5350321,151875880681,
%T A259256 247160867363588025,126888381222131340236953809,
%U A259256 592938336545755964751256254689753896569
%N A259256 With a(1) = 1, a(n) is the smallest number not already in the sequence such that a(n) + Product_{i=1..n-1} a(i) is a square.
%H A259256 Giovanni Resta, <a href="/A259256/b259256.txt">Table of n, a(n) for n = 1..22</a> (terms < 10^1000)
%t A259256 L = {1}; While[Length[L] < 22, p = Times @@ L; q = Ceiling[Sqrt[p + 1]]; While[ MemberQ[L, q^2 - p], q++]; AppendTo[L, q^2 - p]]; L (* _Giovanni Resta_, Jun 22 2015 *)
%o A259256 (PARI) v=[1];n=1;while(n<10^7,s=n+prod(i=1,#v,v[i]);if(issquare(s)&&!vecsearch(vecsort(v),n),v=concat(v,n);n=0);n++);v
%Y A259256 Cf. A259255, A094353, A067836.
%K A259256 nonn,easy
%O A259256 1,2
%A A259256 _Derek Orr_, Jun 22 2015
%E A259256 a(11)-a(14) from _Giovanni Resta_, Jun 22 2015