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 (39,-533,3285,-9594,12636,-5832).
FORMULA
From Philippe Deléham, Apr 04 2013: (Start)
G.f.: 1/(1-x) + 1/(1-2*x) + 1/(1-3*x) + 1/(1-6*x) + 1/(1-9*x) + 1/(1-18*x).
a(n) = 39*a(n-1) -533*a(n-2) +3285*a(n-3) -9594*a(n-4) +12636*a(n-5) -5832*a(n-6) with n>6, a(0)=6, a(1)=39, a(2)=455, a(3)=6813, a(4)= 112931, a(5)=1956669, a(6)=34591115. (End)
MATHEMATICA
Join[{6}, LinearRecurrence[{39, -533, 3285, -9594, 12636, -5832}, {39, 455, 6813, 112931, 1956669, 34591115}, 15]] (* Bruno Berselli, Apr 05 2013 *)
Table[(2^n + 1) (3^n + 9^n + 1), {n, 0, 15}] (* Bruno Berselli, Apr 05 2013 *)
Total[#^Range[0, 20]&/@Divisors[18]] (* Vincenzo Librandi, Apr 17 2014 *)
PROG
(Sage) [sigma(18, n)for n in range(0, 16)] # [Zerinvary Lajos, Jun 04 2009]
(Magma) [DivisorSigma(n, 18): n in [0..20]]; // Bruno Berselli, Apr 05 2013 (improved MAGMA code by Vincenzo Librandi, Apr 17 2014)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved