OFFSET
1,2
LINKS
Colin Barker, Table of n, a(n) for n = 1..490
Index entries for linear recurrences with constant coefficients, signature (1,12098,-12098,-1,1).
FORMULA
a(n) = a(n-1)+12098*a(n-2)-12098*a(n-3)-a(n-4)+a(n-5).
G.f.: -x*(x^4+21*x^3-548*x^2+21*x+1) / ((x-1)*(x^2-110*x+1)*(x^2+110*x+1)).
EXAMPLE
22 is in the sequence because it is the 4th pentagonal number and the 3rd centered heptagonal number.
MATHEMATICA
CoefficientList[Series[(x^4 + 21*x^3 - 548*x^2 + 21*x + 1)/((1 - x)*(x^2 - 110*x + 1)*(x^2 + 110*x + 1)), {x, 0, 20}], x] (* Wesley Ivan Hurt, Jan 19 2017 *)
PROG
(PARI) Vec(-x*(x^4+21*x^3-548*x^2+21*x+1)/((x-1)*(x^2-110*x+1)*(x^2+110*x+1)) + O(x^100))
(Magma) I:=[1, 22, 11572, 265651, 139997551]; [n le 5 select I[n] else Self(n-1)+12098*Self(n-2)-12098*Self(n-3)-Self(n-4)+Self(n-5): n in [1..20]]; // Vincenzo Librandi, Jan 20 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Colin Barker, Feb 04 2015
STATUS
approved