OFFSET
1,1
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (0,0,3).
FORMULA
a(1)=4, a(2)=6, a(3)=9, a(n) = 3*a(n-3) for n>3.
G.f.: x*(4+6*x+9*x^2) / ( 1-3*x^3 ). - R. J. Mathar, Nov 07 2015
MATHEMATICA
NestList[ #+Divisors[ # ][[ -2]]&, 4, 50]
LinearRecurrence[{0, 0, 3}, {4, 6, 9}, 50] (* G. C. Greubel, Apr 17 2016 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Zak Seidov, Sep 29 2009
STATUS
approved