OFFSET
0,1
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..200
Index entries for linear recurrences with constant coefficients, signature (56,-1043,8240,-29204,43904,-21952).
FORMULA
G.f.: 2*(3 - 140*x + 2086*x^2 - 12360*x^3 + 29204*x^4 - 21952*x^5)/((1 - x)*(1 - 2*x)*(1 - 4*x)*(1 - 7*x)*(1 - 14*x)*(1 - 28*x)).
a(n) = (4^n + 2^n + 1)*(7^n + 1).
MATHEMATICA
Total[#^Range[0, 20] & /@ Divisors[28]] (* or *) Table[(4^n + 2^n + 1) (7^n + 1), {n, 0, 20}]
PROG
(Magma) [DivisorSigma(n, 28): n in [0..20]]; /* or */ [(4^n+2^n+1)*(7^n+1): n in [0..20]];
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Apr 17 2014
STATUS
approved