1,1

In other words, numbers n such that n^2 - 1 is the sum of two nonzero distinct squares in exactly one way. This explains why there are many common terms between this sequence and A050797.

Table of n, a(n) for n=1..43.

9 is a term because 9^2 - 1 = (4^2 + 12^2) / 2.

Cf. A050797.

Sequence in context: A190513 A190576 A250663 * A051811 A034056 A195042

Adjacent sequences: A274587 A274588 A274589 * A274591 A274592 A274593

nonn

Altug Alkan, Jun 29 2016

approved