A072574 Triangle T(n,k) of number of compositions (ordered partitions) of n into exactly k distinct parts, 1<=k<=n.
1, 1, 0, 1, 2, 0, 1, 2, 0, 0, 1, 4, 0, 0, 0, 1, 4, 6, 0, 0, 0, 1, 6, 6, 0, 0, 0, 0, 1, 6, 12, 0, 0, 0, 0, 0, 1, 8, 18, 0, 0, 0, 0, 0, 0, 1, 8, 24, 24, 0, 0, 0, 0, 0, 0, 1, 10, 30, 24, 0, 0, 0, 0, 0, 0, 0, 1, 10, 42, 48, 0, 0, 0, 0, 0, 0, 0, 0, 1, 12, 48, 72, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 12, 60, 120, 0
Offset: 1
Examples
T(6,2)=4 since 6 can be written as 1+5=2+4=4+2=5+1. Triangle starts (trailing zeros omitted for n>=10): [ 1] 1; [ 2] 1, 0; [ 3] 1, 2, 0; [ 4] 1, 2, 0, 0; [ 5] 1, 4, 0, 0, 0; [ 6] 1, 4, 6, 0, 0, 0; [ 7] 1, 6, 6, 0, 0, 0, 0; [ 8] 1, 6, 12, 0, 0, 0, 0, 0; [ 9] 1, 8, 18, 0, 0, 0, 0, 0, 0; [10] 1, 8, 24, 24, 0, 0, ...; [11] 1, 10, 30, 24, 0, 0, ...; [12] 1, 10, 42, 48, 0, 0, ...; [13] 1, 12, 48, 72, 0, 0, ...; [14] 1, 12, 60, 120, 0, 0, ...; [15] 1, 14, 72, 144, 120, 0, 0, ...; [16] 1, 14, 84, 216, 120, 0, 0, ...; [17] 1, 16, 96, 264, 240, 0, 0, ...; [18] 1, 16, 114, 360, 360, 0, 0, ...; [19] 1, 18, 126, 432, 600, 0, 0, ...; [20] 1, 18, 144, 552, 840, 0, 0, ...; These rows (without the zeros) are shown in the Richmond/Knopfmacher reference. From _Gus Wiseman_, Oct 17 2022: (Start) Column n = 8 counts the following compositions. (8) (1,7) (1,2,5) (2,6) (1,3,4) (3,5) (1,4,3) (5,3) (1,5,2) (6,2) (2,1,5) (7,1) (2,5,1) (3,1,4) (3,4,1) (4,1,3) (4,3,1) (5,1,2) (5,2,1) (End)
Links
- Joerg Arndt, Table of n, a(n) for n = 1..5050 (rows 1..100, flattened).
- B. Richmond and A. Knopfmacher, Compositions with distinct parts, Aequationes Mathematicae 49 (1995), pp. 86-97.
- Index entries for sequences related to compositions
Crossrefs
Row sums are A032020.
A008289 is the version for partitions (zeros removed).
A072575 counts strict compositions by maximum.
A113704 is the constant instead of strict version.
A216652 is a condensed version (zeros removed).
A336131 counts splittings of partitions with distinct sums.
A336139 counts strict compositions of each part of a strict composition.
Programs
-
Mathematica
Table[Length[Select[Join@@Permutations/@Select[IntegerPartitions[n],UnsameQ@@#&],Length[#]==k&]],{n,0,15},{k,1,n}] (* Gus Wiseman, Oct 17 2022 *)
-
PARI
N=21; q='q+O('q^N); gf=sum(n=0,N, n! * z^n * q^((n^2+n)/2) / prod(k=1,n, 1-q^k ) ); /* print triangle: */ gf -= 1; /* remove row zero */ P=Pol(gf,'q); { for (n=1,N-1, p = Pol(polcoeff(P, n),'z); p += 'z^(n+1); /* preserve trailing zeros */ v = Vec(polrecip(p)); v = vector(n,k,v[k]); /* trim to size n */ print(v); ); } /* Joerg Arndt, Oct 20 2012 */
Formula
T(n, k) = T(n-k, k)+k*T(n-k, k-1) [with T(n, 0)=1 if n=0 and 0 otherwise] = A000142(k)*A060016(n, k).
G.f.: sum(n>=0, n! * z^n * q^((n^2+n)/2) / prod(k=1..n, 1-q^k ) ), rows by powers of q, columns by powers of z; includes row 0 (drop term for n=0 for this triangle, see PARI code); setting z=1 gives g.f. for A032020. [Joerg Arndt, Oct 20 2012]
Comments