

A047694


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


3




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. 925928.
W. Ljunggren, A diophantine problem, J. London Math. Soc. (2), 3 (1971), pp. 385391.


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 * A262016 A129666 A288675
Adjacent sequences: A047691 A047692 A047693 * A047695 A047696 A047697


KEYWORD

sign,fini,full,nice


AUTHOR

N. J. A. Sloane


STATUS

approved



