A154782 Least integer y>=0 such that n+2y^2 is a square; -1 if n is not in A035251.

0, 0, 1, -1, 0, -1, -1, 1, 2, 0, -1, -1, -1, -1, 1, -1, 0, 2, 3, -1, -1, -1, -1, 1, -1, 0, -1, -1, 2, -1, -1, 3, 4, -1, 1, -1, 0, -1, -1, -1, -1, 2, -1, -1, -1, -1, 3, 1, -1, 0, 5, -1, -1, -1, -1, -1, 2, -1, -1, -1, -1, -1, 1, 3, 0, -1, -1, -1, 4, -1, -1, 5, 6, 2, -1, -1, -1, -1, -1, 1, -1, 0

Offset: 0

Author

M. F. Hasler, Jan 19 2009

Keywords

• sign

Crossrefs

Cf. A035251.

Programs

PARI

A154782(n)={for(y=0,sqrtint(n\2),issquare(n+2*y^2)&return(y));-1}