OFFSET
1,3
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..200
Index entries for linear recurrences with constant coefficients, signature (28,-176,320).
FORMULA
a(n) = (11*20^(n-1) - 11*4^(n-1) - 12*(n-1)*4^(n-1))/128. - Andrew Howroyd, May 10 2020
From Colin Barker, Jul 15 2020: (Start)
G.f.: x^2*(1 + 2*x) / ((1 - 4*x)^2*(1 - 20*x)).
a(n) = 28*a(n-1) - 176*a(n-2) + 320*a(n-3) for n>2.
(End)
PROG
(PARI) a(n) = {(11*20^(n-1) - 11*4^(n-1) - 12*(n-1)*4^(n-1))/128} \\ Andrew Howroyd, May 10 2020
(PARI) concat(0, Vec(x^2*(1 + 2*x) / ((1 - 4*x)^2*(1 - 20*x)) + O(x^40))) \\ Colin Barker, Jul 15 2020
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
R. H. Hardin, Dec 06 2008
EXTENSIONS
Terms a(10) and beyond from Andrew Howroyd, May 10 2020
STATUS
approved