OFFSET
0,1
COMMENTS
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (2,-1).
FORMULA
a(n) = (6 + n)*(7 + n)/2 = A000217(6+n) for 0 <= n <= 6, a(n) = a(n-1) + 13 for n >= 7.
G.f.: (21 - 35*x + 15*x^2 - x^8)/(1 - x)^3. - G. C. Greubel, Jul 13 2016
MATHEMATICA
CoefficientList[Series[(21 - 35*x + 15*x^2 - x^8)/(1 - x)^3, {x, 0, 50}], x] (* G. C. Greubel, Jul 13 2016 *)
PROG
(PARI) a(n)=if(n>5, 13*n, n*(n+13)/2+21) \\ Charles R Greathouse IV, Jul 13 2016
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Jaroslav Krizek, Nov 18 2009
STATUS
approved