OFFSET
1,2
COMMENTS
Also positive integers y in the solutions to 6*x^2 - 5*y^2 - 4*x + 5*y - 2 = 0, the corresponding values of x being A253921.
LINKS
Colin Barker, Table of n, a(n) for n = 1..745
Index entries for linear recurrences with constant coefficients, signature (1,482,-482,-1,1).
FORMULA
a(n) = a(n-1)+482*a(n-2)-482*a(n-3)-a(n-4)+a(n-5).
G.f.: x*(55*x^3+241*x^2-55*x-1) / ((x-1)*(x^2-22*x+1)*(x^2+22*x+1)).
EXAMPLE
56 is in the sequence because the 56th centered pentagonal is 7701, which is also the number 51st octagonal number.
MATHEMATICA
CoefficientList[Series[(55 x^3 + 241 x^2 - 55 x - 1)/((x - 1)(x^2 - 22 x + 1) (x^2 + 22 x + 1)), {x, 0, 30}], x] (* Vincenzo Librandi, Jan 20 2015 *)
PROG
(PARI) Vec(x*(55*x^3+241*x^2-55*x-1)/((x-1)*(x^2-22*x+1)*(x^2+22*x+1)) + O(x^100))
(Magma) I:=[1, 56, 297, 26752, 142913]; [n le 5 select I[n] else Self(n-1)+482*Self(n-2)-482*Self(n-3)-Self(n-4)+Self(n-5): n in [1..25]]; // Vincenzo Librandi, Jan 20 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Colin Barker, Jan 19 2015
STATUS
approved