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 A124323 Triangle read by rows: T(n,k) is the number of partitions of an n-set having k singleton blocks (0<=k<=n). 17
 1, 0, 1, 1, 0, 1, 1, 3, 0, 1, 4, 4, 6, 0, 1, 11, 20, 10, 10, 0, 1, 41, 66, 60, 20, 15, 0, 1, 162, 287, 231, 140, 35, 21, 0, 1, 715, 1296, 1148, 616, 280, 56, 28, 0, 1, 3425, 6435, 5832, 3444, 1386, 504, 84, 36, 0, 1, 17722, 34250, 32175, 19440, 8610, 2772, 840, 120, 45, 0, 1 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 0,8 COMMENTS Row sums are the Bell numbers (A000110). T(n,0)=A000296(n). T(n,k) = binomial(n,k)*T(n-k,0). Sum(k*T(n,k),k=0..n) = A052889(n) = n*B(n-1), where B(q) are the Bell numbers (A000110). Exponential Riordan array [exp(exp(x)-1-x),x]. - Paul Barry, Apr 23 2009 Sum_{k=0..n} T(n,k)*2^k = A000110(n+1) is the number of binary relations on an n-set that are both symmetric and transitive. - Geoffrey Critzer, Jul 25 2014 Also the number of set partitions of {1, ..., n} with k cyclical adjacencies (successive elements in the same block, where 1 is a successor of n). Unlike A250104, we count {{1}} as having 1 cyclical adjacency. - Gus Wiseman, Feb 13 2019 REFERENCES T. Mansour, A. O. Munagi, Set partitions with circular successions, European Journal of Combinatorics, 42 (2014), 207-216. LINKS Alois P. Heinz, Rows n = 0..140, flattened David Callan, On conjugates for set partitions and integer compositions, arXiv:math/0508052 [math.CO], 2005. FORMULA T(n,k) = binomial(n,k)*[(-1)^(n-k)+sum((-1)^(j-1)*B(n-k-j), j=1..n-k)], where B(q) are the Bell numbers (A000110). E.g.f.: G(t,z) = exp(exp(z)-1+(t-1)*z)). G.f.: 1/(1-xy-x^2/(1-xy-x-2x^2/(1-xy-2x-3x^2/(1-xy-3x-4x^2/(1-... (continued fraction). - Paul Barry, Apr 23 2009 EXAMPLE T(4,2)=6 because we have 12|3|4, 13|2|4, 14|2|3, 1|23|4, 1|24|3 and 1|2|34 (if we take {1,2,3,4} as our 4-set). Triangle starts:      1      0    1      1    0    1      1    3    0    1      4    4    6    0    1     11   20   10   10    0    1     41   66   60   20   15    0    1    162  287  231  140   35   21    0    1    715 1296 1148  616  280   56   28    0    1   3425 6435 5832 3444 1386  504   84   36    0    1 From Gus Wiseman, Feb 13 2019: (Start) Row n = 5 counts the following set partitions by number of singletons:   {{1234}}    {{1}{234}}  {{1}{2}{34}}  {{1}{2}{3}{4}}   {{12}{34}}  {{123}{4}}  {{1}{23}{4}}   {{13}{24}}  {{124}{3}}  {{12}{3}{4}}   {{14}{23}}  {{134}{2}}  {{1}{24}{3}}                           {{13}{2}{4}}                           {{14}{2}{3}} ... and the following set partitions by number of cyclical adjacencies:   {{13}{24}}      {{1}{2}{34}}  {{1}{234}}  {{1234}}   {{1}{24}{3}}    {{1}{23}{4}}  {{12}{34}}   {{13}{2}{4}}    {{12}{3}{4}}  {{123}{4}}   {{1}{2}{3}{4}}  {{14}{2}{3}}  {{124}{3}}                                 {{134}{2}}                                 {{14}{23}} (End) From Paul Barry, Apr 23 2009: (Start) Production matrix is 0, 1, 1, 0, 1, 1, 2, 0, 1, 1, 3, 3, 0, 1, 1, 4, 6, 4, 0, 1, 1, 5, 10, 10, 5, 0, 1, 1, 6, 15, 20, 15, 6, 0, 1, 1, 7, 21, 35, 35, 21, 7, 0, 1, 1, 8, 28, 56, 70, 56, 28, 8, 0, 1 (End) MAPLE G:=exp(exp(z)-1+(t-1)*z): Gser:=simplify(series(G, z=0, 14)): for n from 0 to 11 do P[n]:=sort(n!*coeff(Gser, z, n)) od: for n from 0 to 11 do seq(coeff(P[n], t, k), k=0..n) od; # yields sequence in triangular form # Program from R. J. Mathar, Jan 22 2015: A124323 := proc(n, k)     binomial(n, k)*A000296(n-k) ; end proc: MATHEMATICA Flatten[CoefficientList[Range[0, 10]! CoefficientList[Series[Exp[x y] Exp[Exp[x] - x - 1], {x, 0, 10}], x], y]] (* Geoffrey Critzer, Nov 24 2011 *) sps[{}]:={{}}; sps[set:{i_, ___}]:=Join@@Function[s, Prepend[#, s]&/@sps[Complement[set, s]]]/@Cases[Subsets[set], {i, ___}]; Table[Length[Select[sps[Range[n]], Count[#, {_}]==k&]], {n, 0, 9}, {k, 0, n}] (* Gus Wiseman, Feb 13 2019 *) CROSSREFS Cf. A000110, A052889, A124324. A250104 is an essentially identical triangle, differing only in row 1. For columns see A000296, A250105, A250106, A250107. Cf. A000126, A001610, A032032, A052841, A066982, A080107, A169985, A187784, A324011, A324014, A324015. Sequence in context: A039727 A137176 A143949 * A250104 A220421 A106683 Adjacent sequences:  A124320 A124321 A124322 * A124324 A124325 A124326 KEYWORD nonn,tabl AUTHOR Emeric Deutsch, Oct 28 2006 STATUS approved

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Last modified November 14 22:45 EST 2019. Contains 329135 sequences. (Running on oeis4.)