The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A173938 The number of permutations avoiding simultaneously consecutive patterns 123 and 231. 2
 1, 1, 2, 4, 11, 39, 161, 784, 4368, 27260, 189540, 1448860, 12076408, 109102564, 1061259548, 11060323280, 122963473024, 1452414435968, 18164949751872, 239807221886128, 3332441297971360, 48624372236312912, 743273838888233264, 11878134680411900928 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Terms a(11) through a(14) calculated by Elizalde and Noy, who state that an involved explicit form for the e.g.f can be found in terms of integrals containing the error function. REFERENCES S. Elizalde and M. Noy, Consecutive patterns in permutations (Theorem 5.1), Adv. Appl. Math. 30 (2003) 110-125. LINKS Alois P. Heinz, Table of n, a(n) for n = 0..200 A. Baxter, B. Nakamura, and D. Zeilberger, Automatic generation of theorems and proofs on enumerating consecutive Wilf-classes S. Kitaev and T. Mansour, On multi-avoidance of generalized patterns, Ars Combinatoria 76 (2005), 321-350 [MR2152770] S. Kitaev and T. Mansour, On multi-avoidance of generalized patterns FORMULA For all n >= 3, A(n)= a(n-1)+a(n;1)+a(n;2)+...+a(n;n-1), where for all 1<= i <= n, a(n;i)= \sum_{j=1}^{i-1} a(n-1;j)+ \sum_{j=i}^{n-2}(n-1-j)*a*(n-2;j), and a(3;1)=1, a(3;2)=1 a(3;3)=2. a(n) ~ c * d^n * n!, where d = A246041 = 0.6948193008667305362671927506... is the root of the equation sqrt(2*Pi)*(erfi(1/sqrt(2)) + erfi((1/d-1)/sqrt(2))) = 2*exp(1/2), c = 1.991594102047693697258367189... . - Vaclav Kotesovec, Aug 23 2014 EXAMPLE Example: For n = 3 a(3) = 4 since 132, 213, 312, and 321 are the 3-permutations avoiding 123 and 231. MAPLE b:= proc(u, o, t) option remember; if(u+o=0, 1,        add(b(u-j, o+j-1, 0), j=1..if(t>0, min(u, t-1), u))+        if(t>0, 0, add(b(u+j-1, o-j, j), j=1..o)))     end: a:= n-> b(n, 0, 0): seq(a(n), n=0..25);  # Alois P. Heinz, Oct 25 2013 MATHEMATICA FullSimplify[CoefficientList[Series[1 + Integrate[(2*Sqrt[E]/(2*Sqrt[E] - Sqrt[2*Pi]*Erfi[1/Sqrt[2]] - Sqrt[2*Pi] * Erfi[(-1+x)/Sqrt[2]]))*((E^(1/2*(-1+x)^2) * (2 + Sqrt[2*E*Pi]*Erf[1/Sqrt[2]] - Pi*Erf[1/Sqrt[2]]*Erfi[1/Sqrt[2]] + Erf[(-1+x)/Sqrt[2]]*(Sqrt[2*E*Pi] - Pi*Erfi[1/Sqrt[2]]) + HypergeometricPFQ[{1, 1}, {3/2, 2}, -1/2] - (-1+x)^2 * HypergeometricPFQ[{1, 1}, {3/2, 2}, -1/2*(-1+x)^2])) / (2*Sqrt[E] - Sqrt[2*Pi]*(Erfi[1/Sqrt[2]] + Erfi[(-1+x)/Sqrt[2]]))), x], {x, 0, 20}], x] *  Range[0, 20]!] (* Vaclav Kotesovec, Aug 22 2014 *) CROSSREFS Sequence in context: A193188 A216810 A065851 * A242790 A013044 A110577 Adjacent sequences:  A173935 A173936 A173937 * A173939 A173940 A173941 KEYWORD nonn AUTHOR Signy Olafsdottir (signy06(AT)ru.is), Mar 03 2010 EXTENSIONS a(15)-a(23) from Alois P. Heinz, Oct 25 2013 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified February 20 12:34 EST 2020. Contains 332076 sequences. (Running on oeis4.)