1,2

Table of n, a(n) for n=1..57.

Select[Range[600], Reduce[#*(2*#-1) == x*(2*x-1) - y*(2*y-1) && x > 0 && y > 0, {x, y}, Integers] == False &]

Cf. A000384 (hexagonal numbers), A135768 (pentagonal case).

Sequence in context: A029748 A018314 A212216 * A215068 A239011 A070525

Adjacent sequences: A199636 A199637 A199638 * A199640 A199641 A199642

nonn

T. D. Noe, Dec 06 2011

approved