A248220 - OEIS

%I #14 Jan 08 2018 01:47:49

%S 1,2,4,7,14,16,25,31,39,48,49,52,57,64,73,74,79,84,86,97,100,112,121,

%T 127,129,134,169,192,194,196,199,217,241,244,254,256,266,273,289,292,

%U 302,304,326,336,337,350,361,372,399,400,409,448,457,484,487,489,511

%N Values of n such that the equation x^2 - n*y^2 = n*(n+1)*(n+2)/6 has integer solutions.

%e 7 is in the sequence because x^2-7*y^2=84 has integer solutions, including (x,y) = (14,4) and (28,10).

%t Select[Range[300],Length[FullSimplify[Solve[x^2-#*y^2==#*(#+1)*(#+2)/6,{x,y},Integers]/.C[1]->1]]>0&] (* _Vaclav Kotesovec_, Oct 05 2014, Mathematica version >= 8 *)

%Y Cf. A000292, A134419, A245226, A248194.

%K nonn

%O 1,2

%A _Colin Barker_, Oct 04 2014

%E More terms from _Vaclav Kotesovec_, Oct 05 2014