A078803 Triangular array T given by T(n,k) = number of compositions of n into k parts, each in the set {1,2,3}.

1, 1, 1, 1, 2, 1, 0, 3, 3, 1, 0, 2, 6, 4, 1, 0, 1, 7, 10, 5, 1, 0, 0, 6, 16, 15, 6, 1, 0, 0, 3, 19, 30, 21, 7, 1, 0, 0, 1, 16, 45, 50, 28, 8, 1, 0, 0, 0, 10, 51, 90, 77, 36, 9, 1, 0, 0, 0, 4, 45, 126, 161, 112, 45, 10, 1, 0, 0, 0, 1, 30, 141, 266, 266, 156, 55, 11, 1, 0, 0, 0, 0, 15, 126

Offset: 1

Author

Clark Kimberling, Dec 06 2002

Keywords

• nonn
• tabl

Comments

Number of lattice paths from (0,0) to (n,k) using steps (1,1), (2,1), (3,1). - Joerg Arndt, Jul 05 2011

Reversing the rows produces A078802. Row sums: A000073.

Number of tribonacci binary words of length n-1 having k-1 1's. A tribonacci binary word is a binary word having no three consecutive 0's. Example: T(6,3)=7 because we have 00101,00110,01001,01010,01100,10010 and 10100. - Emeric Deutsch, Jun 16 2007

This is the Riordan array (1,x+x^2+x^3)(A071675) without its column k=0. - Vladimir Kruchinin, Feb 10 2011

Examples

			T(5,2) = 2 counts the compositions 2+3 and 3+2.
Triangle begins
  1;
  1, 1;
  1, 2, 1;
  0, 3, 3, 1;
  0, 2, 6, 4, 1;
  0, 1, 7, 10, 5, 1;
  0, 0, 6, 16, 15, 6, 1;
  0, 0, 3, 19, 30, 21, 7, 1;
  0, 0, 1, 16, 45, 50, 28, 8, 1;
  0, 0, 0, 10, 51, 90, 77, 36, 9, 1;
  0, 0, 0, 4, 45, 126, 161, 112, 45, 10, 1;
  0, 0, 0, 1, 30, 141, 266, 266, 156, 55, 11, 1;
		

References

• Clark Kimberling, Binary words with restricted repetitions and associated compositions of integers, in Applications of Fibonacci Numbers, vol.10, Proceedings of the Eleventh International Conference on Fibonacci Numbers and Their Applications, William Webb, editor, Congressus Numerantium, Winnipeg, Manitoba 194 (2009) 141-151.

Links

• Alois P. Heinz, Rows n = 1..141, flattened
• Jean Luc Baril, Rigoberto Flórez, and José L. Ramirez, Generalized Narayana arrays, restricted Dyck paths, and related bijections, Univ. Bourgogne (France, 2025). See p. 18.
• Vladimir Kruchinin, Composition of ordinary generating functions, arXiv:1009.2565 [math.CO], 2010.

Crossrefs

Cf. A027907, A078802, A030528 (parts <=2), A213887 (parts <=4), A213888 (parts <=5), A061676 and A213889 (parts <=6).

Programs

Maple

A078803 := proc(n,k) add( binomial(j,n-3*k+2*j)*binomial(k,j),j=0..k) ; end proc:
# R. J. Mathar, Feb 22 2011

Mathematica

nn=8;CoefficientList[Series[1/(1-y(x+x^2+x^3)),{x,0,nn}],{x,y}]//Grid (* Geoffrey Critzer, Jan 08 2013 *)

Formula

T(n, k) = t(n-1, n-k), for 1<=k<=n, for n>=1, where the array t is given by A078802.

G.f.: 1/(1-t*z*(1+z+z^2))-1. - Emeric Deutsch, Mar 10 2004

T(n,k) = Sum_{j=0..k} C(j,n-3*k+2*j)*C(k,j). - Vladimir Kruchinin, Feb 10 2011

Extensions

More terms from Emeric Deutsch, Jun 16 2007