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).
KEYWORD
nonn,base
AUTHOR
N. J. A. Sloane, Nov 19 2018
STATUS
approved