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.

1, 3, 6, 7, 18, 36, 148, 5625, 351225, 5350321, 151875880681, 247160867363588025, 126888381222131340236953809, 592938336545755964751256254689753896569

Offset

1,2

Links

Giovanni Resta, Table of n, a(n) for n = 1..22 (terms < 10^1000)

Mathematica

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 *)

Prog

(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

Crossrefs

Cf. A259255, A094353, A067836.

Sequence in context: A130049 A333553 A341183 * A056703 A113534 A103831

Adjacent sequences: A259253 A259254 A259255 * A259257 A259258 A259259

Keyword

nonn,easy

Author

Derek Orr, Jun 22 2015

Extensions

a(11)-a(14) from Giovanni Resta, Jun 22 2015

Status

approved