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A129922 Number of 3-Carlitz compositions of n (or, more generally p-Carlitz compositions, p > 1), i.e., words b_1^{i_1}b_2^{i_2}...b_k^{i_k} such that the b_j's and i_j's are positive integers for which Sum_{j=1..k} i_j * b_j = n and, for all j, i_j < p and if b_j = b_(j+1) then i_j + i_(j+1) is not equal to p. 2
1, 1, 3, 4, 12, 22, 51, 101, 225, 465, 1008, 2111, 4528, 9560, 20402, 43222, 92018, 195256, 415243, 881758, 1874288, 3981318, 8460906, 17975132, 38196045, 81152769, 172436680, 366376845, 778476016, 1654054258, 3514494256, 7467412436, 15866507485, 33712418692, 71630875356, 152198161794 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

For p=2, the sequence enumerates Carlitz compositions, A003242.

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..1000

Sylvie Corteel, PaweĊ‚ Hitczenko, Generalizations of Carlitz Compositions, Journal of Integer Sequences, Vol. 10 (2007), Article 07.8.8.

FORMULA

G.f.: 1/(1 - Sum_{k>0} (z^k/(1-z^k) - 3*z^(k*3)/(1-z^(k*3)))).

For general p the generating function is 1/(1 - Sum_{k>0}(z^k/(1-z^k) - p*z^(k*p)/(1-z^(k*p)))).

EXAMPLE

a(3)=4 because, for p=3, we can write:

  3^{1},

  1^{1} 2^{1},

  2^{1} 1^{1},

  1^{1} 1^{1} 1^{1}.

MAPLE

b:= proc(n, i, j) option remember;

     `if`(n=0, 1, add(add(`if`(k=i and m+j=3, 0,

      b(n-k*m, k, m)), m=1..min(2, n/k)), k=1..n))

    end:

a:= n-> b(n, 0$2):

seq(a(n), n=0..40);  # Alois P. Heinz, Jul 22 2017

PROG

(PARI) N = 66;  x = 'x + O('x^N);  p=3;

gf = 1/(1-sum(k=1, N, x^k/(1-x^k)-p*x^(k*p)/(1-x^(k*p))));

Vec(gf)  /* Joerg Arndt, Apr 28 2013 */

CROSSREFS

Cf. A129921.

Cf. A003242.

Sequence in context: A075220 A075221 A295948 * A005221 A243391 A000206

Adjacent sequences:  A129919 A129920 A129921 * A129923 A129924 A129925

KEYWORD

nonn

AUTHOR

Pawel Hitczenko (phitczenko(AT)math.drexel.edu), Jun 05 2007

EXTENSIONS

Added more terms, Joerg Arndt, Apr 28 2013

STATUS

approved

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Last modified January 17 10:30 EST 2019. Contains 319218 sequences. (Running on oeis4.)