OFFSET
6,3
COMMENTS
It would be nice to have a more precise definition.
The g.f. is not D-finite.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 6..1000
Srecko Brlek, Andrea Frosini, Simone Rinaldi, and Laurent Vuillon, Tilings by translation: enumeration by a rational language approach, The Electronic Journal of Combinatorics, vol. 13, (2006). See Section 4.2.
FORMULA
G.f.: Sum_{k>=1} k*x^(3*(k+1))/(1-x^(k+1))^2. - Andrew Howroyd, Oct 31 2018
MAPLE
seq(coeff(series(add(k*x^(3*(k+1))/(1-x^(k+1))^2, k=1..n), x, n+1), x, n), n = 6 .. 75); # Muniru A Asiru, Oct 31 2018
MATHEMATICA
kmax = 80;
Sum[k*x^(3*(k+1))/(1-x^(k+1))^2, {k, 1, kmax}] + O[x]^kmax // CoefficientList[#, x]& // Drop[#, 6]& (* Jean-François Alcover, Sep 10 2019 *)
PROG
(PARI) seq(n)={Vec(sum(k=1, ceil(n/3), k*x^(3*(k+1))/(1-x^(k+1))^2 + O(x^(6+n))))} \\ Andrew Howroyd, Oct 31 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Oct 30 2018
EXTENSIONS
Terms a(33) and beyond from Andrew Howroyd, Oct 31 2018
STATUS
approved