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 A231602 Triangular array read by rows: T(n,k) is the number of rooted labeled trees on n nodes that have exactly k nodes with outdegree = 1, n>=1, 0<=k<=n-1. 3
 1, 0, 2, 3, 0, 6, 4, 36, 0, 24, 65, 80, 360, 0, 120, 306, 1950, 1200, 3600, 0, 720, 4207, 12852, 40950, 16800, 37800, 0, 5040, 38424, 235592, 359856, 764400, 235200, 423360, 0, 40320, 573057, 2766528, 8481312, 8636544, 13759200, 3386880, 5080320, 0, 362880 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS T(n,k) is also the number of functions f:{1,2,...,n-1}->{1,2,...,n} that have exactly k elements whose preimage has cardinality = 1. T(n,n-1) = n! = A000142(n). Column k = 0 = A060356(n). Row sums = n^(n-1) = A000169(n). Refinement given by A248120. Sum coefficients of the partition polynomials with h_1 = (1') = t and all other h_n = (n') = 1 to obtain this entry. - Tom Copeland, Feb 01 2016 LINKS Alois P. Heinz, Rows n = 1..141, flattened FORMULA E.g.f. satisfies A(x,y) = y*x*A(x,y) + x*( exp(A(x,y)) - A(x,y) ). EXAMPLE 1; 0, 2; 3, 0, 6; 4, 36, 0, 24; 65, 80, 360, 0, 120; 306, 1950, 1200, 3600, 0, 720; 4207, 12852, 40950, 16800, 37800, 0, 5040; 38424, 235592, 359856, 764400, 235200, 423360, 0, 40320; ....0..........0........ ....|........./ \....... ....0........0...0...... .../ \.......|.......... ..0   0......0.......... T(4,1) = 36.  Both of these graphs on 4 nodes have exactly 1 node that has outdegree = 1.  There are 12 + 24 = 36 labelings. MAPLE with(combinat): C:= binomial: b:= proc(t, i, u) option remember; `if`(t=0, 1,       `if`(i<2, 0, b(t, i-1, u) +add(multinomial(t, t-i*j, i\$j)       *b(t-i*j, i-1, u-j)*u!/(u-j)!/j!, j=1..t/i)))     end: T:= (n, k)-> C(n, k)*C(n-1, k)*k! *b(n-1-k\$2, n-k): seq(seq(T(n, k), k=0..n-1), n=1..10);  # Alois P. Heinz, Nov 12 2013 MATHEMATICA nn=8; Table[Table[Drop[Range[0, nn]!CoefficientList[Series[-ProductLog[x/(-1-x+x y)], {x, 0, nn}], {x, y}], 1][[r, c]], {c, 1, r}], {r, 1, nn}]//Grid CROSSREFS Cf. A055302, A206823. Cf. A248120. Sequence in context: A173717 A058301 A199601 * A097287 A233672 A233670 Adjacent sequences:  A231599 A231600 A231601 * A231603 A231604 A231605 KEYWORD nonn,tabl AUTHOR Geoffrey Critzer, Nov 11 2013 STATUS approved

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Last modified January 21 08:09 EST 2020. Contains 331104 sequences. (Running on oeis4.)