Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #64 Sep 08 2022 08:44:40
%S 0,0,0,0,1,10,71,448,2710,16285,99179,619784,4005585,26901537,
%T 188224882,1373263700,10444784477,82735225014,681599167459,
%U 5830974941867,51717594114952,474845349889731,4506624255883683,44151662795470696,445957579390657965
%N Number of crossing set partitions of {1,2,...,n}.
%C A partition p of the set N_n = {1,2,...,n}, whose elements are arranged in their natural order, is crossing if there exist four numbers 1 <= i < k < j < l <= n such that i and j are in the same block, k and l are in the same block, but i,j and k,l belong to two different blocks. Noncrossing partitions are also called "planar rhyme schemes". - _Peter Luschny_, Apr 28 2011
%C Consider a set of A000217(n) balls of n colors in which, for each integer k = 1 to n, exactly one color appears in the set a total of k times. (Each ball has exactly one color and is indistinguishable from other balls of the same color.) a(n+1) equals the number of ways to choose 0 or more balls of each color while satisfying the following conditions:
%C 1. No two colors are chosen the same positive number of times.
%C 2. Among colors chosen at least once, there exists at least one pair of colors (c, d) such that color c is chosen more times than color d, but color d appears more times in the original set than color c.
%C If the second requirement is removed, the number of acceptable ways to choose equals A000110(n+1). The number of ways that meet the first requirement, but fail to meet the second, equals A000108(n+1). See related comment for A085082. - _Matthew Vandermast_, Nov 22 2010
%C In the May 1978 Scientific American, Martin Gardner mentions Lady Murasaki's The Tale of Genji in which chapter heads illustrate A000110(5) = 52. These are the "crossing" cases mentioned there as being discussed by JoAnne Growney's 1970 thesis. - _Alford Arnold_, expanded by _Charles R Greathouse IV_, Jun 21 2021
%D JoAnne (Simpson) Growney, Structure Inherent in a Free Groupoid, PhD Dissertation, The University of Oklahoma, 1970.
%H T. D. Noe, <a href="/A016098/b016098.txt">Table of n, a(n) for n = 0..100</a>
%H H. W. Becker, <a href="https://doi.org/10.1090/S0002-9904-1952-09547-1">Planar rhyme schemes</a>, in The October meeting in Washington, Bull. Amer. Math. Soc. 58 (1952) p. 39.
%H Martin Gardner, <a href="https://www.jstor.org/stable/24955724">Mathematical Games</a>, Scientific American (May 1978), pp. 24-32.
%H G. Kreweras, <a href="http://dx.doi.org/10.1016/0012-365X(72)90041-6">Sur les partitions non croisées d'un cycle</a>, (French) Discrete Math. 1 (1972), no. 4, 333-350. MR0309747 (46 #8852).
%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Noncrossing_partition">Noncrossing partition</a>
%F a(n) = A000110(n) - A000108(n).
%F a(n) = Sum_{k=0..n} S2(n,k) - binomial(2*n,n)/(n+1); S2(n,k) Stirling numbers of the second kind.
%F E.g.f.: exp(exp(x)-1) - (BesselI(0,2*x) - BesselI(1,2*x))*exp(2*x). - _Ilya Gutkovskiy_, Aug 31 2016
%e 13|24 is the only crossing partition of {1,2,3,4}.
%e G.f. = x^4 + 10*x^5 + 71*x^6 + 448*x^7 + 2710*x^8 + 16285*x^9 + ...
%e From _Gus Wiseman_, Feb 15 2019: (Start)
%e The a(5) = 10 crossing set partitions:
%e {{1,2,4},{3,5}}
%e {{1,3},{2,4,5}}
%e {{1,3,4},{2,5}}
%e {{1,3,5},{2,4}}
%e {{1,4},{2,3,5}}
%e {{1},{2,4},{3,5}}
%e {{1,3},{2,4},{5}}
%e {{1,3},{2,5},{4}}
%e {{1,4},{2},{3,5}}
%e {{1,4},{2,5},{3}}
%e (End)
%p A016098 := n -> combinat[bell](n) - binomial(2*n,n)/(n+1):
%p seq(A016098(n),n=0..22); # _Peter Luschny_, Apr 28 2011
%t Table[Sum[StirlingS2[n, k], {k, 0, n}] - Binomial[2*n, n]/(n + 1), {n, 0, 25}] (* _T. D. Noe_, May 29 2012 *)
%t Table[BellB[n] - CatalanNumber[n], {n, 0, 40}] (* _Vincenzo Librandi_, Aug 31 2016 *)
%t sps[{}]:={{}};sps[set:{i_,___}]:=Join@@Function[s,Prepend[#,s]&/@sps[Complement[set,s]]]/@Cases[Subsets[set],{i,___}];
%t croXQ[stn_]:=MatchQ[stn,{___,{___,x_,___,y_,___},___,{___,z_,___,t_,___},___}/;x<z<y<t||z<x<t<y];
%t Table[Length[Select[sps[Range[n]],croXQ]],{n,0,10}] (* _Gus Wiseman_, Feb 17 2019 *)
%o (MuPAD) combinat::bell(n)-combinat::catalan(n) $ n = 0..26 // _Zerinvary Lajos_, May 10 2008
%o (Sage) [bell_number(i)-catalan_number(i) for i in range(23)] # _Zerinvary Lajos_, Mar 14 2009
%o (Magma) [Bell(n)-Catalan(n): n in [0..25]]; // _Vincenzo Librandi_, Aug 31 2016
%Y Cf. A000108, A000110, A001006, A001263, A080107, A125181, A134264, A194560, A306417, A306437.
%K nonn
%O 0,6
%A _Robert G. Wilson v_
%E Offset corrected by _Matthew Vandermast_, Nov 22 2010
%E New name from _Peter Luschny_, Apr 28 2011