OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..9603
FORMULA
G.f. A(x) satisfies: A(x) = (1 + x + 2*x^2 + 3*x^3 + 4*x^4 + 5*x^5 + 6*x^6) * A(x^7).
MATHEMATICA
Table[Times @@ DeleteCases[IntegerDigits[n, 7], 0], {n, 0, 80}]
nmax = 80; A[_] = 1; Do[A[x_] = (1 + x + 2 x^2 + 3 x^3 + 4 x^4 + 5 x^5 + 6 x^6) A[x^7] + O[x]^(nmax + 1) // Normal, nmax + 1]; CoefficientList[A[x], x]
PROG
(PARI) a(n) = vecprod(select(x->x, digits(n, 7))); \\ Michel Marcus, Nov 14 2020
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Ilya Gutkovskiy, Nov 13 2020
STATUS
approved