OFFSET
0,1
LINKS
T. D. Noe, Table of n, a(n) for n=0..200
Index entries for linear recurrences with constant coefficients, signature (32,-262,672,-441).
FORMULA
a(n) = (1+3^n)*(1+7^n). - Bruno Berselli, Apr 17 2014
G.f.: -4*(168*x^3-131*x^2+24*x-1) / ((x-1)*(3*x-1)*(7*x-1)*(21*x-1)). - Colin Barker, May 03 2014
MATHEMATICA
Total[#^Range[0, 20]&/@Divisors[21]] (* Vincenzo Librandi, Apr 17 2014 *)
Table[(1 + 3^n) (1 + 7^n), {n, 0, 20}] (* Bruno Berselli, Apr 17 2014 *)
PROG
(Sage) [sigma(21, n)for n in range(0, 16)] # Zerinvary Lajos, Jun 04 2009
(Magma) [DivisorSigma(n, 21): n in [0..15]]; // Vincenzo Librandi, Apr 17 2014
(PARI) s=[]; for(n=0, 30, s=concat(s, sigma(21, n))); s \\ Colin Barker, May 03 2014
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved