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Number T(n,k) of set partitions of [n] with symmetric block size list of length k; triangle T(n,k), n>=0, 0<=k<=n, read by rows.
13

%I #23 Nov 27 2024 11:56:46

%S 1,0,1,0,1,1,0,1,0,1,0,1,3,2,1,0,1,0,7,0,1,0,1,10,19,13,3,1,0,1,0,56,

%T 0,22,0,1,0,1,35,160,171,86,34,4,1,0,1,0,463,0,470,0,50,0,1,0,1,126,

%U 1337,2306,2066,1035,250,70,5,1,0,1,0,3874,0,10299,0,2160,0,95,0,1

%N Number T(n,k) of set partitions of [n] with symmetric block size list of length k; triangle T(n,k), n>=0, 0<=k<=n, read by rows.

%H Alois P. Heinz, <a href="/A275281/b275281.txt">Rows n = 0..200, flattened</a>

%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Partition_of_a_set">Partition of a set</a>

%F T(n,k) = 0 if n is odd and k is even.

%e T(4,2) = 3: 12|34, 13|24, 14|23.

%e T(5,3) = 7: 12|3|45, 13|2|45, 1|234|5, 1|235|4, 14|2|35, 1|245|3, 15|2|34.

%e T(6,4) = 13: 12|3|4|56, 13|2|4|56, 1|23|45|6, 1|23|46|5, 14|2|3|56, 1|24|35|6, 1|24|36|5, 1|25|34|6, 1|26|34|5, 15|2|3|46, 1|25|36|4, 1|26|35|4, 16|2|3|45.

%e T(7,5) = 22: 12|3|4|5|67, 13|2|4|5|67, 1|23|4|56|7, 1|23|4|57|6, 14|2|3|5|67, 1|24|3|56|7, 1|24|3|57|6, 1|2|345|6|7, 1|2|346|5|7, 1|2|347|5|6, 15|2|3|4|67, 1|25|3|46|7, 1|25|3|47|6, 1|2|356|4|7, 1|2|357|4|6, 1|26|3|45|7, 1|27|3|45|6, 16|2|3|4|57, 1|26|3|47|5, 1|2|367|4|5, 1|27|3|46|5, 17|2|3|4|56.

%e Triangle T(n,k) begins:

%e 1;

%e 0, 1;

%e 0, 1, 1;

%e 0, 1, 0, 1;

%e 0, 1, 3, 2, 1;

%e 0, 1, 0, 7, 0, 1;

%e 0, 1, 10, 19, 13, 3, 1;

%e 0, 1, 0, 56, 0, 22, 0, 1;

%e 0, 1, 35, 160, 171, 86, 34, 4, 1;

%e 0, 1, 0, 463, 0, 470, 0, 50, 0, 1;

%e 0, 1, 126, 1337, 2306, 2066, 1035, 250, 70, 5, 1;

%e ...

%p b:= proc(n, s) option remember; expand(`if`(n>s,

%p binomial(n-1, n-s-1)*x, 1)+add(binomial(n-1, j-1)*

%p b(n-j, s+j)*binomial(s+j-1, j-1), j=1..(n-s)/2)*x^2)

%p end:

%p T:= n-> (p-> seq(coeff(p, x, i), i=0..n))(b(n, 0)):

%p seq(T(n), n=0..12);

%t b[n_, s_] := b[n, s] = Expand[If[n>s, Binomial[n-1, n-s-1]*x, 1] + Sum[ Binomial[n-1, j-1]*b[n-j, s+j]*Binomial[s+j-1, j-1], {j, 1, (n-s)/2} ]*x^2]; T[n_] := Function[p, Table[Coefficient[p, x, i], {i, 0, n}]][b[n, 0]]; Table[T[n], {n, 0, 12}] // Flatten (* _Jean-François Alcover_, Feb 03 2017, translated from Maple *)

%Y Columns k=0-1,3,5,7,9 give: A000007, A000012 for n>0, A275289, A275290, A275291, A275292.

%Y Bisections of columns k=2,4,6,8,10 give: A001700(n-1) for n>0, A275293, A275294, A275295, A275296.

%Y Row sums give A275282.

%Y T(n,A004525(n)) gives A305197.

%Y T(2n,n) gives A275283.

%Y T(2n+1,A109613(n)) gives A305198.

%Y T(n,n) gives A000012.

%Y T(n+3,n+1) gives A002623.

%K nonn,tabl

%O 0,13

%A _Alois P. Heinz_, Jul 21 2016