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 A006957 Self-convolution of numbers of preferential arrangements. 5
 1, 2, 7, 32, 185, 1310, 11067, 109148, 1234045, 15752858, 224169407, 3518636504, 60381131265, 1124390692886, 22577494959427, 486212633129300, 11177317486573445, 273173247028616594, 7072436847620016327 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..200 FORMULA a(n) ~ n! / (log(2))^(n+1). - Vaclav Kotesovec, Nov 08 2014 G.f.: (Sum_{j>=0} j!*x^j / Product_{k=1..j} (1 - k*x))^2. - Ilya Gutkovskiy, Apr 06 2019 MAPLE f:= proc(n) option remember; `if`(n<=1, 1,       add(binomial(n, k) *f(n-k), k=1..n))     end: a:= n-> add(f(k)*f(n-k), k=0..n): seq(a(n), n=0..25);  # Alois P. Heinz, Feb 02 2009 MATHEMATICA t[n_] := Sum[StirlingS2[n, k]*k!, {k, 0, n}]; Table[Sum[t[k]*t[n-k], {k, 0, n}], {n, 0, 20}] (* Jean-François Alcover, Apr 09 2014, after Emanuele Munarini *) PROG (Maxima) t(n):=sum(stirling2(n, k)*k!, k, 0, n); makelist(sum(t(k)*t(n-k), k, 0, n), n, 0, 20); \\ Emanuele Munarini, Oct 02 2012 CROSSREFS Cf. A000670, A217388, A217389. Sequence in context: A000153 A006154 A000987 * A189780 A195983 A079265 Adjacent sequences:  A006954 A006955 A006956 * A006958 A006959 A006960 KEYWORD nonn AUTHOR EXTENSIONS More terms from Alois P. Heinz, Feb 02 2009 STATUS approved

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Last modified October 13 23:56 EDT 2019. Contains 327983 sequences. (Running on oeis4.)