A076674 Smallest a(n)>a(n-1) such that a(n)^2+a(n-1)^2 is a perfect square, a(1)=9.

9, 12, 16, 30, 40, 42, 56, 90, 120, 126, 168, 224, 360, 378, 504, 550, 1320, 1386, 1848, 1989, 2652, 2961, 3948, 5264, 8052, 9711, 12948, 17264, 24852, 31311, 41748, 53289, 71052, 94736, 130548, 145061, 146280, 153594, 163392, 170280, 173290

Offset: 1

Author

Zak Seidov, Oct 25 2002

Keywords

• nonn

Comments

The sequence is infinite.

Crossrefs

Cf. A076600.

Programs

Mathematica

ps[n_]:=Module[{k=n+1,n2=n^2},While[!IntegerQ[Sqrt[n2+k^2]],k++];k]; NestList[ ps,9,40] (* Harvey P. Dale, May 01 2014 *)

Formula

a(n)=A076671(n), n>1. [From R. J. Mathar, Sep 20 2008]