A270471 Expansion of g.f. (1-3*x)/(1-7*x).

1, 4, 28, 196, 1372, 9604, 67228, 470596, 3294172, 23059204, 161414428, 1129900996, 7909306972, 55365148804, 387556041628, 2712892291396, 18990246039772, 132931722278404, 930522055948828, 6513654391641796, 45595580741492572, 319169065190448004, 2234183456333136028

Offset

0,2

Comments

After 1, is this A208704?

Links

Colin Barker, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (7).

Formula

G.f.: (1-3*x)/(1-7*x).

a(n) = 7*a(n-1) for n>1.

a(n) = 4*7^(n-1) for n>0.

E.g.f.: (4*exp(7*x) + 3)/7. - Elmo R. Oliveira, Mar 25 2025

Mathematica

CoefficientList[Series[(1 - 3 x)/(1 - 7 x), {x, 0, 21}], x] (* Michael De Vlieger, Mar 18 2016 *)
Join[{1}, NestList[7#&, 4, 20]] (* Harvey P. Dale, Dec 21 2019 *)

Prog

(PARI) Vec((1-3*x)/(1-7*x) + O(x^30))

Crossrefs

Cf. A208704.

Cf. A000420 (powers of 7), A083076 (partial sums).

Cf. A193577: (1-2*x)/(1-7*x); A169634: (1-4*x)/(1-7*x).

Sequence in context: A218175 A002903 A208704 * A355354 A019482 A198630

Adjacent sequences: A270468 A270469 A270470 * A270472 A270473 A270474

Keyword

nonn,easy

Author

Colin Barker, Mar 17 2016

Status

approved