OFFSET
0,2
COMMENTS
For n>0, a(n) is the sum of the numbers from 2n+2 to 4n. The last digit of a(n) corresponds to the last digit of the squares mod 10 (A008959). Binomial Transform of a(n) starts: -1, 3, 28, 124, 432, 1328, 3776, 10176, 26368, ... . - Wesley Ivan Hurt, Dec 06 2014
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (3,-3,1).
FORMULA
G.f.: (-1+7*x+6*x^2)/(1-x)^3. - Vincenzo Librandi, Jul 07 2012
a(n) = 3*a(n-1) -3*a(n-2) +a(n-3). - Vincenzo Librandi, Jul 07 2012
E.g.f.: (-1+5*x+6*x^2)*e^x. - Robert Israel, Dec 07 2014
Sum_{n>=0} 1/a(n) = 2/5*(log(2)-1) -sqrt(3)*Pi/30 -3*log(3)/10 = -0.6337047... - R. J. Mathar, Apr 22 2024
MAPLE
MATHEMATICA
CoefficientList[Series[(-1+7*x+6*x^2)/(1-x)^3, {x, 0, 50}], x] (* Vincenzo Librandi, Jul 07 2012 *)
PROG
(Magma) [(2*n-1)*(3*n+1): n in [0..50]]; // Vincenzo Librandi, Jul 07 2012
(Haskell)
a033569 n = (2 * n - 1) * (3 * n + 1)
a033569_list = map a033569 [0..]
-- Reinhard Zumkeller, Jul 05 2015
(PARI) a(n)=(2*n-1)*(3*n+1) \\ Charles R Greathouse IV, Jun 17 2017
(Sage) [(2*n-1)*(3*n+1) for n in (0..50)] # G. C. Greubel, Apr 02 2019
(GAP) List([0..50], n-> (2*n-1)*(3*n+1)) # G. C. Greubel, Apr 02 2019
CROSSREFS
KEYWORD
sign,easy
AUTHOR
STATUS
approved