A001027 Powers of 18.

1, 18, 324, 5832, 104976, 1889568, 34012224, 612220032, 11019960576, 198359290368, 3570467226624, 64268410079232, 1156831381426176, 20822964865671168, 374813367582081024, 6746640616477458432, 121439531096594251776, 2185911559738696531968, 39346408075296537575424, 708235345355337676357632, 12748236216396078174437376

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Comments

Same as Pisot sequences E(1, 18), L(1, 18), P(1, 18), T(1, 18). Essentially same as Pisot sequences E(18, 324), L(18, 324), P(18, 324), T(18, 324). See A008776 for definitions of Pisot sequences.

The compositions of n in which each natural number is colored by one of p different colors are called p-colored compositions of n. For n>=1, a(n) equals the number of 18-colored compositions of n such that no adjacent parts have the same color. - Milan Janjic, Nov 17 2011

References

• N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

• T. D. Noe, Table of n, a(n) for n = 0..100
• P. J. Cameron, Sequences realized by oligomorphic permutation groups, J. Integ. Seqs. Vol. 3 (2000), #00.1.5.
• INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 282
• Tanya Khovanova, Recursive Sequences
• Simon Plouffe, Approximations de séries génératrices et quelques conjectures, Dissertation, Université du Québec à Montréal, 1992; arXiv:0911.4975 [math.NT], 2009.
• Simon Plouffe, 1031 Generating Functions, Appendix to Thesis, Montreal, 1992
• Y. Puri and T. Ward, Arithmetic and growth of periodic orbits, J. Integer Seqs., Vol. 4 (2001), #01.2.1.
• Index entries for linear recurrences with constant coefficients, signature (18).

Programs

Magma

[ 18^n: n in [0..20] ]; // Vincenzo Librandi, Nov 21 2010

Maple

A001027:=-1/(-1+18*z); # Simon Plouffe in his 1992 dissertation

Mathematica

Table[18^n,{n,0,40}] (* Vladimir Joseph Stephan Orlovsky, Feb 15 2011 *)

PARI

a(n)=18^n \\ Charles R Greathouse IV, Sep 28 2015

Sage

[18**n for n in range(20)] # F. Chapoton, Feb 23 2020

Sage

[lucas_number1(n,18,0) for n in range(1, 17)] # Zerinvary Lajos, Apr 29 2009

Formula

G.f.: 1/(1-18x), e.g.f.: exp(18x).

a(n) = 18^n; a(n) = 18*a(n-1) with a(0)=1. - Vincenzo Librandi, Nov 21 2010

Extensions

More terms from James Sellers, Sep 19 2000