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 A055924 Exponential transform of Stirling-1 triangle A008275. 2
 1, -1, 2, 2, -6, 5, -6, 22, -30, 15, 24, -100, 175, -150, 52, -120, 548, -1125, 1275, -780, 203, 720, -3528, 8120, -11025, 9100, -4263, 877, -5040, 26136, -65660, 101535, -101920, 65366, -24556, 4140, 40320, -219168, 590620, -1009260 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS |a(n,k)| = number of sets of permutations of {1,...,n} with k total cycles. Comments from David Callan, Sep 20 2007: (Start) |a(n,k)| = stirling1(n, k) * bell(k) counts the above sets of permutations. To see this, recall that stirling1(n, k) is the number of permutations of [n]={1,...,n} with k cycles and bell(k) is the number of set partitions of [k]. Given such a permutation and set partition, write the permutation in standard cycle form (smallest entry first in each cycle and first entries decreasing left to right). For example, with n=15 and k=6, {{10}, {6, 11}, {5, 7, 15}, {3, 13, 12, 8}, {2, 14, 9}, {1, 4}} is in this standard cycle form. Then combine cycles as specified by the partition to form a set of lists. For example, the partition 156-24-3 would yield {{10, 2, 14, 9, 1, 4}, {6, 11, 3, 13, 12, 8}, {5, 7, 15}}. The original first entries are now the record left-to-right lows. Finally, apply to each list the well known transformation that sends # record lows to # cycles. The example yields {{4, 14, 1, 2, 10, 9}, {13, 11, 3, 6, 8, 12}, {7, 15, 5}}. This is a bijection to sets of lists (i.e. permutations) with a total of k cycles, as required. (End) LINKS FORMULA E.g.f.: exp((1+x)^y-1). a(n, k) = stirling1(n, k) * bell(k). - Vladeta Jovovic, Feb 01 2003 EXAMPLE 1; -1,2; 2,-6,5; -6,22,-30,15; 24,-100,175,-150,52; ... |a(3,2)|=6 because (12)(3), (12)|(3), (13)(2), (13)|(2), (23)(1), (23)|(1). CROSSREFS Row sums of |a(n, k)| give A000262. Cf. A008275, A008297, A055925. Sequence in context: A200226 A300628 A115255 * A286278 A156563 A201500 Adjacent sequences:  A055921 A055922 A055923 * A055925 A055926 A055927 KEYWORD sign,tabl AUTHOR Wouter Meeussen, Christian G. Bower, Jul 06 2000 STATUS approved

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Last modified September 27 15:29 EDT 2020. Contains 337383 sequences. (Running on oeis4.)