A047694 x such that y^2 = C(x,0) + C(x,1) + C(x,2) + C(x,3) is soluble.

-1, 0, 2, 7, 15, 74, 767

Offset

0,3

Comments

n such that A000125(n) is a perfect square. - Frank M Jackson, Mar 13 2013

References

R. K. Guy, Unsolved Problems in Number Theory, Section D3.

Links

Table of n, a(n) for n=0..6.

Andrew Bremner, An equation of Mordell, Math. Comp., 29 (1975), pp. 925-928.

W. Ljunggren, A diophantine problem, J. London Math. Soc. (2), 3 (1971), pp. 385-391.

Formula

x such that 6y^2 = (x + 1)(x^2 - x + 6) has solutions in integers.

Mathematica

Select[Range[-10, 10^3], IntegerQ[Sqrt[((# + 1)(#^2 - # + 6))/6]] &] (* Alonso del Arte, Sep 13 2011 *)

Crossrefs

Cf. A047695.

Sequence in context: A282197 A050612 A120110 * A338399 A262016 A129666

Adjacent sequences: A047691 A047692 A047693 * A047695 A047696 A047697

Keyword

sign,fini,full,nice

Author

N. J. A. Sloane

Status

approved