A321542 a(0)=1; thereafter a(n) = 3*a(n-1) with digits rearranged into nondecreasing order.

1, 3, 9, 27, 18, 45, 135, 45, 135, 45, 135, 45, 135, 45, 135, 45, 135, 45, 135, 45, 135, 45, 135, 45, 135, 45, 135, 45, 135, 45, 135, 45, 135, 45, 135, 45, 135, 45, 135, 45, 135, 45, 135, 45, 135, 45, 135, 45, 135, 45, 135, 45, 135

Offset

0,2

Comments

For n >= 5, alternates between 45 and 135.

Links

Paolo Xausa, Table of n, a(n) for n = 0..10000

Index entries for linear recurrences with constant coefficients, signature (0,1).

Formula

G.f.: (-117*x^6 - 18*x^5 - 9*x^4 - 24*x^3 - 8*x^2 - 3*x - 1)/(x^2 - 1). - Chai Wah Wu, Nov 20 2018

Mathematica

A321542list[nmax_]:=PadRight[{1, 3, 9, 27, 18}, nmax+1, {135, 45}]; A321542list[100] (* Paolo Xausa, Aug 10 2023 *)

Crossrefs

The following are parallel families: A000079 (2^n), A004094 (2^n reversed), A028909 (2^n sorted up), A028910 (2^n sorted down), A036447 (double and reverse), A057615 (double and sort up), A263451 (double and sort down); A000244 (3^n), A004167 (3^n reversed), A321540 (3^n sorted up), A321539 (3^n sorted down), A163632 (triple and reverse), A321542 (triple and sort up), A321541 (triple and sort down).

Sequence in context: A131997 A122842 A070358 * A321540 A036123 A168427

Adjacent sequences: A321539 A321540 A321541 * A321543 A321544 A321545

Keyword

nonn,base

Author

N. J. A. Sloane, Nov 19 2018

Status

approved