A076671 Smallest a(n) > a(n-1) such that a(n)^2+a(n-1)^2 is a perfect square, with a(1)=5.

5, 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.

If we require the terms to be distinct, but not necessarily increasing, then the sequence "paints itself into a corner" and can't be continued: 5, 12, 9, 40, 30, 16, 63, 60, 11. - Ivan Neretin, Dec 15 2016

Links

• Ivan Neretin, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A076600.

Programs

Mathematica

Nest[Append[#, k = #[[-1]]; d = Divisors[k^2]; Min@Select[(Reverse@d - d)/2, IntegerQ@# && # > k &]] &, {5}, 40] (* Ivan Neretin, Dec 15 2016 *)