OFFSET
1,1
COMMENTS
Positive integers x in the solutions to 2*x^2-194*y^2-18624*y-599072 = 0.
LINKS
Colin Barker, Table of n, a(n) for n = 1..370
Index entries for linear recurrences with constant coefficients, signature (0,0,125619266,0,0,-1).
FORMULA
a(n) = 125619266*a(n-3)-a(n-6).
G.f.: -679*x*(x-1)*(x^4+2277*x^3+5415742*x^2+2277*x+1) / (x^6-125619266*x^3+1).
EXAMPLE
679 is in the sequence because 679^2 = 461041 = 15^2+16^2+...+111^2.
MATHEMATICA
LinearRecurrence[{0, 0, 125619266, 0, 0, -1}, {679, 1545404, 3675742735, 81619738879, 194132514608060, 461744104375531831}, 30] (* Vincenzo Librandi, May 11 2015 *)
Rest[CoefficientList[Series[-679x(x-1)(x^4+2277x^3+5415742x^2+ 2277x+1)/ (x^6-125619266x^3+1), {x, 0, 15}], x]] (* Harvey P. Dale, Aug 02 2021 *)
PROG
(PARI) Vec(-679*x*(x-1)*(x^4+2277*x^3+5415742*x^2+2277*x+1) / (x^6-125619266*x^3+1) + O(x^100))
(Magma) I:=[679, 1545404, 3675742735, 81619738879, 194132514608060, 461744104375531831]; [n le 6 select I[n] else 125619266*Self(n-3)-Self(n-6): n in [1..20]]; // Vincenzo Librandi, May 11 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Colin Barker, May 10 2015
STATUS
approved