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 A143396 Triangle T(n,k) = number of forests of labeled rooted trees of height at most 1, with n labels, k of which are used for root nodes and any root may contain >= 1 labels, n >= 0, 0<=k<=n. 12
 1, 0, 1, 0, 2, 2, 0, 3, 9, 5, 0, 4, 30, 40, 15, 0, 5, 90, 220, 185, 52, 0, 6, 255, 1040, 1485, 906, 203, 0, 7, 693, 4550, 9905, 9891, 4718, 877, 0, 8, 1820, 19040, 59850, 87416, 66808, 26104, 4140, 0, 9, 4644, 77448, 341082, 686826, 750120, 463212, 153063, 21147 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 LINKS Alois P. Heinz, Rows n = 0..140, flattened FORMULA T(n,k) = C(n,k) * Sum_{t=0..k} stirling2(k,t) * t^(n-k). E.g.f.: exp(exp(x)*(exp(x*y)-1)). - Vladeta Jovovic, Dec 08 2008 EXAMPLE T(3,2) = 9: {1,2}<-3, {1,3}<-2, {2,3}<-1, {1}<-3{2}, {1}{2}<-3, {1}<-2{3}, {1}{3}<-2, {2}<-1{3}, {2}{3}<-1. Triangle begins:   1;   0,  1;   0,  2,  2;   0,  3,  9,   5;   0,  4, 30,  40,  15;   0,  5, 90, 220, 185,  52; MAPLE T:= (n, k)-> binomial(n, k)*add(Stirling2(k, t)*t^(n-k), t=0..k): seq(seq(T(n, k), k=0..n), n=0..11); MATHEMATICA Unprotect[Power]; 0^0 = 1; T[n_, k_] := T[n, k] = Binomial[n, k]*Sum[ StirlingS2[k, t]*t^(n-k), {t, 0, k}]; Table[T[n, k], {n, 0, 11}, {k, 0, n}] // Flatten (* Jean-François Alcover, May 27 2016, translated from Maple *) CROSSREFS Columns k=0-10 give: A000007, A000027, A273652, A273653, A273654, A273655, A273656, A273657, A273658, A273659, A273660. Diagonal gives A000110. Row sums give A143405. T(2n,n) gives A273661. Cf. A048993, A008277, A007318. Sequence in context: A065484 A255970 A011137 * A244129 A090657 A167001 Adjacent sequences:  A143393 A143394 A143395 * A143397 A143398 A143399 KEYWORD nonn,tabl AUTHOR Alois P. Heinz, Aug 12 2008 STATUS approved

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Last modified October 18 04:54 EDT 2019. Contains 328145 sequences. (Running on oeis4.)