OFFSET
0,2
LINKS
FORMULA
a(n) = C(n, 0) + 11C(n, 1) + 9C(n, 2); binomial transform of (1, 11, 9, 0, 0, 0, ...).
a(n) = (9n^2 + 13n+2)/2.
G.f.: (1 + 9x - x^2)/(1-x)^3.
a(n) = 9*n + a(n-1) + 2 (with a(0)=1). - Vincenzo Librandi, Aug 08 2010
EXAMPLE
a(1) = 9*1 + 1 + 2 = 12;
a(2) = 9*2 + 12 + 2 = 32;
a(3) = 9*3 + 32 + 2 = 61.
PROG
(PARI) a(n)=(9*n^2+13*n+2)/2 \\ Charles R Greathouse IV, Jun 17 2017
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Mar 15 2003
STATUS
approved