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A215861
Number T(n,k) of simple labeled graphs on n nodes with exactly k connected components that are trees or cycles; triangle T(n,k), n>=0, 0<=k<=n, read by rows.
18
1, 0, 1, 0, 1, 1, 0, 4, 3, 1, 0, 19, 19, 6, 1, 0, 137, 135, 55, 10, 1, 0, 1356, 1267, 540, 125, 15, 1, 0, 17167, 15029, 6412, 1610, 245, 21, 1, 0, 264664, 218627, 90734, 23597, 3990, 434, 28, 1, 0, 4803129, 3783582, 1515097, 394506, 70707, 8694, 714, 36, 1
OFFSET
0,8
COMMENTS
Also the Bell transform of A215851(n+1). For the definition of the Bell transform see A264428 and the links given there. - Peter Luschny, Jan 21 2016
LINKS
FORMULA
T(0,0) = 1, T(n,k) = 0 for k<0 or k>n, and otherwise T(n,k) = Sum_{i=0..n-k} C(n-1,i)*T(n-1-i,k-1)*h(i) with h(i) = 1 for i<2 and h(i) = i!/2 + (i+1)^(i-1) else.
EXAMPLE
T(4,2) = 19:
.1 2. .1 2. .1-2. .1-2. .1 2. .1 2. .1 2. .1 2. .1 2. .1 2.
. /|. .|\ . .|/ . . \|. . /|. . |. . / . .|\ . . \ . .| .
.4-3. .4-3. .4 3. .4 3. .4 3. .4-3. .4-3. .4 3. .4-3. .4-3.
.
.1-2. .1-2. .1 2. .1-2. .1-2. .1 2. .1-2. .1 2. .1 2.
.| . . / . .|/ . . \ . . |. . \|. . . .| |. . X .
.4 3. .4 3. .4 3. .4 3. .4 3. .4 3. .4-3. .4 3. .4 3.
Triangle T(n,k) begins:
1;
0, 1;
0, 1, 1;
0, 4, 3, 1;
0, 19, 19, 6, 1;
0, 137, 135, 55, 10, 1;
0, 1356, 1267, 540, 125, 15, 1;
0, 17167, 15029, 6412, 1610, 245, 21, 1;
...
MAPLE
T:= proc(n, k) option remember; `if`(k<0 or k>n, 0,
`if`(n=0, 1, add(binomial(n-1, i)*T(n-1-i, k-1)*
`if`(i<2, 1, i!/2 +(i+1)^(i-1)), i=0..n-k)))
end:
seq(seq(T(n, k), k=0..n), n=0..12);
# Alternatively, with the function BellMatrix defined in A264428:
BellMatrix(n -> `if`(n<2, 1, n!/2+(n+1)^(n-1)), 8); # Peter Luschny, Jan 21 2016
MATHEMATICA
t[0, 0] = 1; t[n_, k_] /; k < 0 || k > n = 0; t[n_, k_] := t[n, k] =Sum[ Binomial[n-1, i]*t[n-1-i, k-1]* If[i < 2, 1, i!/2 + (i+1)^(i-1)], {i, 0, n-k}]; Table[t[n, k], {n, 0, 9}, {k, 0, n}] // Flatten (* Jean-François Alcover, Jun 07 2013 *)
(* Alternatively, with the function BellMatrix defined in A264428: *)
g[n_] = If[n < 2, 1, n!/2 + (n+1)^(n-1)]; BellMatrix[g, 8] (* Peter Luschny, Jan 21 2016 *)
rows = 11;
t = Table[If[n<2, 1, n!/2 + (n+1)^(n-1)], {n, 0, rows}];
T[n_, k_] := BellY[n, k, t];
Table[T[n, k], {n, 0, rows}, {k, 0, n}] // Flatten (* Jean-François Alcover, Jun 22 2018, after Peter Luschny *)
PROG
(Sage) # uses[bell_matrix from A264428]
bell_matrix(lambda n: factorial(n)//2 + (n+1)^(n-1) if n>=2 else 1, 8) # Peter Luschny, Jan 21 2016
CROSSREFS
Diagonal and lower diagonals give: A000012, A000217, A215862, A215863, A215864, A215865.
Row sums give: A144164.
T(2n,n) gives A309313.
Sequence in context: A117026 A316656 A083904 * A327366 A327069 A327334
KEYWORD
nonn,tabl
AUTHOR
Alois P. Heinz, Aug 25 2012
STATUS
approved