A047695 y such that y^2 = C(x,0) + C(x,1) + C(x,2) + C(x,3) is soluble.

0, 1, 2, 8, 24, 260, 8672

Offset

0,3

References

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

Links

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

Mathematica

r[x_] := Reduce[y >= 0 && 6*y^2 == (x + 1)*(x^2 - x + 6), {y}, Integers]; Reap[ Do[ If[r[x] =!= False, Sow[y /. ToRules[r[x]]]], {x, -10, 1000}]][[2, 1]] (* Jean-François Alcover, Jul 12 2012 *)

Crossrefs

Cf. A047694.

Sequence in context: A214849 A141598 A071599 * A093842 A331001 A050971

Adjacent sequences: A047692 A047693 A047694 * A047696 A047697 A047698

Keyword

nonn,fini,full,nice

Author

N. J. A. Sloane

Status

approved