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
1 |23
2 |13
3 |12
123
so there are 7 elements in the first (smallest) blocks, 7 in the second blocks and only 1 in the third blocks.
Triangle T(n,k) begins:
1;
3, 1;
7, 7, 1;
21, 25, 13, 1;
66, 101, 71, 21, 1;
258, 366, 396, 166, 31, 1;
1079, 1555, 1877, 1247, 337, 43, 1;
4987, 7099, 9199, 7855, 3305, 617, 57, 1;
25195, 34627, 47371, 47245, 27085, 7681, 1045, 73, 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>n, 0,
add((p-> p+`if`(t>0 and t-j<1, [0, p[1]*i], 0))(b(n-i*j, i+1,
max(0, t-j))/j!*combinat[multinomial](n, i$j, n-i*j)), j=0..n/i)))
end:
T:= (n, k)-> b(n, 1, 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, {}]];
Table[T[n], {n, 1, 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