OFFSET
1,2
LINKS
Alois P. Heinz, Rows n = 1..141, flattened
Wikipedia, Partition of a set
EXAMPLE
The 5 set partitions of {1,2,3} are:
1 |2 |3
12 |3
13 |2
23 |1
123
so there are 10 elements in the first (largest) blocks, 4 in the second blocks and only 1 in the third blocks.
Triangle T(n,k) begins:
1;
3, 1;
10, 4, 1;
35, 17, 7, 1;
136, 76, 36, 11, 1;
577, 357, 186, 81, 16, 1;
2682, 1737, 1023, 512, 162, 22, 1;
13435, 8997, 5867, 3151, 1345, 295, 29, 1;
72310, 49420, 34744, 20071, 10096, 3145, 499, 37, 1;
...
MAPLE
b:= proc(n, l) option remember; `if`(n=0, add(l[-i]*
x^i, i=1..nops(l)), add(binomial(n-1, j-1)*
b(n-j, sort([l[], j])), j=1..n))
end:
T:= n-> (p-> (seq(coeff(p, x, i), i=1..n)))(b(n, [])):
seq(T(n), n=1..12);
# second Maple program:
b:= proc(n, i, t) option remember; `if`(n=0, [1, 0], `if`(i<1, 0,
add((p-> p+`if`(t>0 and t-j<1, [0, p[1]*i], 0))(
combinat[multinomial](n, i$j, n-i*j)/j!*
b(n-i*j, min(n-i*j, i-1), max(0, t-j))), j=0..n/i)))
end:
T:= (n, k)-> b(n$2, k)[2]:
seq(seq(T(n, k), k=1..n), n=1..12); # Alois P. Heinz, Mar 02 2020
MATHEMATICA
b[n_, l_] := b[n, l] = If[n == 0, Sum[l[[-i]] x^i, {i, 1, Length[l]}], Sum[ Binomial[n-1, j-1] b[n-j, Sort[Append[l, j]]], {j, 1, n}]];
T[n_] := Function[p, Table[Coefficient[p, x, i], {i, 1, n}]][b[n, {}]];
Array[T, 12] // Flatten (* Jean-François Alcover, Dec 28 2018, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn,tabl
AUTHOR
Alois P. Heinz, Dec 07 2018
STATUS
approved