OFFSET
1,2
LINKS
Derek Kinsella, Plane division by lines and circles. [Wayback Machine link]
Index entries for linear recurrences with constant coefficients, signature (3,-3,1).
FORMULA
A007318 * [1, 3, 7, 0, 0, 0, ...].
O.g.f.: x*(1 + x + 5x^2)/(1-x)^3. - R. J. Mathar, May 06 2008
a(n) = 7*n^2/2 - 15*n/2 + 5 = 3*a(n-1) - 3*a(n-2) + a(n-3). - R. J. Mathar, Jul 31 2009
a(n) = a(n-1) + 7*n - 11 (with a(1)=1). - Vincenzo Librandi, Nov 24 2010
EXAMPLE
a(4) = 31 = (1, 3, 3, 1) dot (1, 3, 7, 0) = (1 + 9 + 21 + 0).
MATHEMATICA
s = 1; lst = {s}; Do[s += n + 2; AppendTo[lst, s], {n, 1, 265, 7}]; lst (* Zerinvary Lajos, Jul 11 2009 *)
PROG
(PARI) a(n)=n*(7*n-15)/2+5 \\ Charles R Greathouse IV, Jun 17 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Gary W. Adamson, May 03 2008
EXTENSIONS
More terms from R. J. Mathar, May 06 2008
STATUS
approved