OFFSET
0,2
FORMULA
Sum_{n>=0} 1/a(n) = log(3).
G.f.: (1+8x+63x^2+8x^3+x^4)/(1-x)^4.
a(n) = A027480(3n-1), n>0. - R. J. Mathar, Apr 07 2009
Sum_{n>=0} (-1)^n/a(n) = 4*log(2)/3. - Amiram Eldar, Feb 27 2022
MATHEMATICA
nxt[{n_, a_}]:={n+1, ((3n)(3n-1)(3n+1))/2}; NestList[nxt, {0, 1}, 40][[All, 2]]/.(0->Nothing) (* Harvey P. Dale, Sep 24 2016 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaume Oliver Lafont, Feb 21 2009
STATUS
approved