cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-8 of 8 results.

A000179 Ménage numbers: a(0) = 1, a(1) = -1, and for n >= 2, a(n) = number of permutations s of [0, ..., n-1] such that s(i) != i and s(i) != i+1 (mod n) for all i.

Original entry on oeis.org

1, -1, 0, 1, 2, 13, 80, 579, 4738, 43387, 439792, 4890741, 59216642, 775596313, 10927434464, 164806435783, 2649391469058, 45226435601207, 817056406224416, 15574618910994665, 312400218671253762, 6577618644576902053, 145051250421230224304, 3343382818203784146955, 80399425364623070680706, 2013619745874493923699123
Offset: 0

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Author

Keywords

Comments

According to rook theory, John Riordan considered a(1) to be -1. - Vladimir Shevelev, Apr 02 2010
This is also the value that the formulas of Touchard and of Wyman and Moser give and is compatible with many recurrences. - William P. Orrick, Aug 31 2020
Or, for n >= 3, the number of 3 X n Latin rectangles the second row of which is full cycle with a fixed order of its elements, e.g., the cycle (x_2,x_3,...,x_n,x_1) with x_1 < x_2 < ... < x_n. - Vladimir Shevelev, Mar 22 2010
Muir (p. 112) gives essentially this recurrence (although without specifying any initial conditions). Compare A186638. - N. J. A. Sloane, Feb 24 2011
Sequence discovered by Touchard in 1934. - L. Edson Jeffery, Nov 13 2013
Although these are also known as Touchard numbers, the problem was formulated by Lucas in 1891, who gave the recurrence formula shown below. See Cerasoli et al., 1988. - Stanislav Sykora, Mar 14 2014
An equivalent problem was formulated by Tait; solutions to Tait's problem were given by Muir (1878) and Cayley (1878). - William P. Orrick, Aug 31 2020
From Vladimir Shevelev, Jun 25 2015: (Start)
According to the ménage problem, 2*n!*a(n) is the number of ways of seating n married couples at 2*n chairs around a circular table, men and women in alternate positions, so that no husband is next to his wife.
It is known [Riordan, ch. 7] that a(n) is the number of arrangements of n non-attacking rooks on the positions of the 1's in an n X n (0,1)-matrix A_n with 0's in positions (i,i), i = 1,...,n, (i,i+1), i = 1,...,n-1, and (n,1). This statement could be written as a(n) = per(A_n). For example, A_5 has the form
001*11
1*0011
11001* (1)
11*100
0111*0,
where 5 non-attacking rooks are denoted by {1*}.
We can indicate a one-to-one correspondence between arrangements of n non-attacking rooks on the 1's of a matrix A_n and arrangements of n married couples around a circular table by the rules of the ménage problem, after the ladies w_1, w_2, ..., w_n have taken the chairs numbered
2*n, 2, 4, ..., 2*n-2 (2)
respectively. Suppose we consider an arrangement of rooks: (1,j_1), (2,j_2), ..., (n,j_n). Then the men m_1, m_2, ..., m_n took chairs with numbers
2*j_i - 3 (mod 2*n), (3)
where the residues are chosen from the interval[1,2*n]. Indeed {j_i} is a permutation of 1,...,n. So {2*j_i-3}(mod 2*n) is a permutation of odd positive integers <= 2*n-1. Besides, the distance between m_i and w_i cannot be 1. Indeed, the equality |2*(j_i-i)-1| = 1 (mod 2*n) is possible if and only if either j_i=i or j_i=i+1 (mod n) that correspond to positions of 0's in matrix A_n.
For example, in the case of positions of {1*} in(1) we have j_1=3, j_2=1, j_3=5, j_4=2, j_5=4. So, by(2) and (3) the chairs 1,2,...,10 are taken by m_4, w_2, m_1, w_3, m_5, w_4, m_3, w_5, m_2, w_1, respectively. (End)
The first 20 terms of this sequence were calculated in 1891 by E. Lucas (see [Lucas, p. 495]). - Peter J. C. Moses, Jun 26 2015
From Ira M. Gessel, Nov 27 2018: (Start)
If we invert the formula
Sum_{ n>=0 } u_n z^n = ((1-z)/(1+z)) F(z/(1+z)^2)
that Don Knuth mentions (see link) (i.e., set x=z/(1+z)^2 and solve for z in terms of x), we get a formula for F(z) = Sum_{n >= 0} n! z^n as a sum with all positive coefficients of (almost) powers of the Catalan number generating function.
The exact formula is (5) of the Yiting Li article.
This article also gives a combinatorial proof of this formula (though it is not as simple as one might want). (End)

Examples

			a(2) = 0; nothing works. a(3) = 1; (201) works. a(4) = 2; (2301), (3012) work. a(5) = 13; (20413), (23401), (24013), (24103), (30412), (30421), (34012), (34021), (34102), (40123), (43012), (43021), (43102) work.
		

References

  • W. W. R. Ball and H. S. M. Coxeter, Mathematical Recreations and Essays, 13th Ed. Dover, p. 50.
  • M. Cerasoli, F. Eugeni and M. Protasi, Elementi di Matematica Discreta, Nicola Zanichelli Editore, Bologna 1988, Chapter 3, p. 78.
  • L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 185, mu(n).
  • Kaplansky, Irving and Riordan, John, The probleme des menages, Scripta Math. 12, (1946). 113-124. See u_n.
  • E. Lucas, Théorie des nombres, Paris, 1891, pp. 491-495.
  • P. A. MacMahon, Combinatory Analysis. Cambridge Univ. Press, London and New York, Vol. 1, 1915 and Vol. 2, 1916; see vol. 1, p 256.
  • T. Muir, A Treatise on the Theory of Determinants. Dover, NY, 1960, Sect. 132, p. 112. - N. J. A. Sloane, Feb 24 2011
  • J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, p. 197.
  • V. S. Shevelev, Reduced Latin rectangles and square matrices with equal row and column sums, Diskr. Mat. (J. of the Akademy of Sciences of Russia) 4(1992), 91-110. - Vladimir Shevelev, Mar 22 2010
  • N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
  • H. M. Taylor, A problem on arrangements, Mess. Math., 32 (1902), 60ff.
  • J. Touchard, Permutations discordant with two given permutations, Scripta Math., 19 (1953), 108-119.
  • J. H. van Lint, Combinatorial Theory Seminar, Eindhoven University of Technology, Springer Lecture Notes in Mathematics, Vol. 382, 1974. See page 10.

Crossrefs

Diagonal of A058087. Also a diagonal of A008305.
A000179, A102761, and A335700 are all essentially the same sequence but with different conventions for the initial terms a(0) and a(1). - N. J. A. Sloane, Aug 06 2020

Programs

  • Haskell
    import Data.List (zipWith5)
    a000179 n = a000179_list !! n
    a000179_list = 1 : -1 : 0 : 1 : zipWith5
       (\v w x y z -> (x * y + (v + 2) * z - w) `div` v) [2..] (cycle [4,-4])
       (drop 4 a067998_list) (drop 3 a000179_list) (drop 2 a000179_list)
    -- Reinhard Zumkeller, Aug 26 2013
    
  • Maple
    A000179:= n ->add ((-1)^k*(2*n)*binomial(2*n-k,k)*(n-k)!/(2*n-k), k=0..n); # for n >= 1
    U:= proc(n) local k; add( (2*n/(2*n-k))*binomial(2*n-k,k)*(n-k)!*(x-1)^k, k=0..n); end; W := proc(r,s) coeff( U(r),x,s ); end; A000179 := n->W(n,0); # valid for n >= 1
  • Mathematica
    a[n_] := 2*n*Sum[(-1)^k*Binomial[2*n - k, k]*(n - k)!/(2*n - k), {k, 0, n}]; a[0] = 1; Table[a[n], {n, 0, 21}] (* Jean-François Alcover, Dec 05 2012, from 2nd formula *)
  • PARI
    \\ 3 programs adapted to a(1) = -1 by Hugo Pfoertner, Aug 31 2020
    
  • PARI
    {a(n) = my(A); if( n, A = vector(n,i,i-2); for(k=4, n, A[k] = (k * (k - 2) * A[k-1] + k * A[k-2] - 4 * (-1)^k) / (k-2)); A[n], 1)};/* Michael Somos, Jan 22 2008 */
    
  • PARI
    a(n)=if(n>1, round(2*n*exp(-2)*besselk(n, 2)), 1-2*n) \\ Charles R Greathouse IV, Nov 03 2014
    
  • PARI
    {a(n) = my(A); if( n, A = vector(n,i,i-2); for(k=5, n, A[k] = k * A[k-1] + 2 * A[k-2] + (4-k) * A[k-3] - A[k-4]); A[n], 1)} /* Michael Somos, May 02 2018 */
    
  • Python
    from math import comb, factorial
    def A000179(n): return 1 if n == 0 else sum((-2*n if k & 1 else 2*n)*comb(m:=2*n-k,k)*factorial(n-k)//m for k in range(n+1)) # Chai Wah Wu, May 27 2022

Formula

a(n) = ((n^2-2*n)*a(n-1) + n*a(n-2) - 4*(-1)^n)/(n-2) for n >= 3.
a(n) = A059375(n)/(2*n!) for n >= 2.
a(n) = Sum_{k=0..n} (-1)^k*(2*n)*binomial(2*n-k, k)*(n-k)!/(2*n-k) for n >= 1. - Touchard (1934)
G.f.: ((1-x)/(1+x))*Sum_{n>=0} n!*(x/(1+x)^2)^n. - Vladeta Jovovic, Jun 26 2007
a(2^k+2) == 0 (mod 2^k); for k >= 2, a(2^k) == 2(mod 2^k). - Vladimir Shevelev, Jan 14 2011
a(n) = round( 2*n*exp(-2)*BesselK(n,2) ) for n > 1. - Mark van Hoeij, Oct 25 2011
a(n) ~ (n/e)^n * sqrt(2*Pi*n)/e^2. - Charles R Greathouse IV, Jan 21 2016
0 = a(n)*(-a(n+2) +a(n+4)) +a(n+1)*(+a(n+1) +a(n+2) -3*a(n+3) -5*a(n+4) +a(n+5)) +a(n+2)*(+2*a(n+2) +3*a(n+3) -3*a(n+4)) +a(n+3)*(+2*a(n+3) +a(n+4) -a(n+5)) +a(n+4)*(+a(n+4)), for all n>1. If a(-2..1) = (0, -1, 2, -1) then also true for those values of n. - Michael Somos, Apr 29 2018
D-finite with recurrence: 0 = a(n) +n*a(n+1) -2*a(n+2) +(-n-4)*a(n+3) +a(n+4), for all n in Z where a(n) = a(-n) for all n in Z and a(0) = 2, a(1) = -1. - Michael Somos, May 02 2018
a(n) = Sum_{k=0..n} A213234(n,k) * A000023(n-2*k) = Sum_{k=0..n} (-1)^k * n/(n-k) * binomial(n-k, k) * (n-2*k)! Sum_{j=0..n-2*k} (-2)^j/j! for n >= 1. [Wyman and Moser (1958)]. - William P. Orrick, Jun 25 2020
a(k+4*p) - 2*a(k+2*p) + a(k) is divisible by p, for any k > 0 and any prime p. - Mark van Hoeij, Jan 11 2022

Extensions

More terms from James Sellers, May 02 2000
Additional comments from David W. Wilson, Feb 18 2003
a(1) changed to -1 at the suggestion of Don Knuth. - N. J. A. Sloane, Nov 26 2018

A258664 A total of n married couples, including a mathematician M and his wife, are to be seated at the 2n chairs around a circular table, with no man seated next to his wife. After the ladies are seated at every other chair, M is the first man allowed to choose one of the remaining chairs. The sequence gives the number of ways of seating the other men, with no man seated next to his wife, if M chooses the chair that is 3 seats clockwise from his wife's chair.

Original entry on oeis.org

0, 0, 1, 1, 4, 20, 115, 787, 6184, 54888, 542805, 5916725, 70463900, 910167596, 12672415015, 189181881575, 3014307220880, 51054940726928, 915987174021609, 17352888926841897, 346144782915314740, 7251738265074465220, 159193007549552845339, 3654204694819144118651
Offset: 1

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Author

Keywords

Comments

This is a variation of the classic ménage problem (cf. A000179).
It is known [Riordan, ch. 8, ex. 7(b)] that, after the ladies are seated at every other chair, the number U_n of ways of seating the men in the ménage problem has asymptotic expansion U_n ~ e^(-2)*n!*(1 + Sum_{k>=1}(-1)^k/(k!(n-1)_k)), where (n)_k = n*(n-1)*...*(n-k+1).
Therefore, it is natural to conjecture that a(n) ~ e^(-2)*n!/(n-2)*(1 + Sum_{k>=1}(-1)^k/(k!(n-1)_k)).

References

  • I. Kaplansky and J. Riordan, The problème des ménages, Scripta Math. 12, (1946), 113-124.
  • J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, chs. 7, 8.

Crossrefs

Programs

  • Mathematica
    a[d_,n_]:=If[n<=#-1,0,Sum[((-1)^k)*(n-k-1)!Sum[Binomial[2#-j-4,j]*Binomial[2(n-#)-k+j+2,k-j],{j,Max[#+k-n-1,0],Min[k,#-2]}],{k,0,n-1}]]&[(d+3)/2];
    Map[a[3,#]&,Range[25]] (* Peter J. C. Moses, Jun 07 2015 *)
  • PARI
    a(n) = sum(k=0, n-1, (-1)^k*(n-k-1)!*sum(j=max(k-n+2, 0), min(k,1), binomial(2-j, j)*binomial(2*n-k+j-4, k-j))); \\ Michel Marcus, Jun 26 2015

Formula

a(n) = Sum_{0<=k<=n-1}(-1)^k*(n-k-1)! * Sum_{max(k-n+2, 0)<=j<=min(k,1)} binomial(2-j, j)*binomial(2*n-k+j-4, k-j).

A258666 A total of n married couples, including a mathematician M and his wife, are to be seated at the 2n chairs around a circular table, with no man seated next to his wife. After the ladies are seated at every other chair, M is the first man allowed to choose one of the remaining chairs. The sequence gives the number of ways of seating the other men, with no man seated next to his wife, if M chooses the chair that is 7 seats clockwise from his wife's chair.

Original entry on oeis.org

0, 0, 0, 0, 4, 20, 117, 791, 6204, 55004, 543595, 5922925, 70518884, 910711076, 12678337153, 189252394275, 3015217877068, 51067618521276, 916176420499159, 17355904074255065, 346195849623668420, 7252654428822549364, 159210363264445218829, 3654550887654460566191
Offset: 1

Views

Author

Keywords

Comments

This is a variation of the classic ménage problem (cf. A000179).
It is known [Riordan, ch. 8, ex. 7(b)] that, after the ladies are seated at every other chair, the number U_n of ways of seating the men in the ménage problem has asymptotic expansion U_n ~ e^(-2)*n!*(1 + Sum_{k>=1} (-1)^k/(k!(n-1)_k)), where (n)_k = n*(n-1)*...*(n-k+1).
Therefore, it is natural to conjecture that a(n) ~ e^(-2)*n!/(n-2)*(1 + Sum_{k>=1} (-1)^k/(k!(n-1)_k)).

References

  • I. Kaplansky and J. Riordan, The problème des ménages, Scripta Math. 12, (1946), 113-124.
  • J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, chs. 7, 8.

Crossrefs

Programs

  • Mathematica
    a[n_] := If[n<5, 0, Sum[(-1)^k (n-k-1)! Sum[Binomial[6-j, j] Binomial[2n-k+j-8, k-j], {j, Max[k-n+4, 0], Min[k, 3]}], {k, 0, n-1}]];
    Array[a, 24] (* Jean-François Alcover, Sep 19 2018 *)
  • PARI
    vector(30, n, if (n<=4, 0, sum(k=0,n-1,(-1)^k*(n-k-1)!*sum(j=max(k-n+4, 0),min(k,3), binomial(6-j, j)*binomial(2*n-k+j-8, k-j))))) \\ Michel Marcus, Jun 17 2015

Formula

a(n)=0 for n <= 4; for n >= 5, a(n) = Sum_{k=0..n-1} (-1)^k*(n-k-1)! Sum_{j=max(k-n+4, 0)..min(k,3)} binomial(6-j, j)*binomial(2*n-k+j-8, k-j).

A258667 A total of n married couples, including a mathematician M and his wife, are to be seated at the 2n chairs around a circular table, with no man seated next to his wife. After the ladies are seated at every other chair, M is the first man allowed to choose one of the remaining chairs. The sequence gives the number of ways of seating the other men, with no man seated next to his wife, if M chooses the chair that is 9 seats clockwise from his wife's chair.

Original entry on oeis.org

0, 0, 0, 0, 0, 20, 116, 791, 6205, 55004, 543596, 5922929, 70518903, 910711188, 12678337924, 189252400363, 3015217931281, 51067619058668, 916176426367084, 17355904144230373, 346195850528456683, 7252654441430368404, 159210363452786908116, 3654550890657000160319
Offset: 1

Views

Author

Keywords

Comments

This is a variation of the classic ménage problem (cf. A000179).
It is known [Riordan, ch. 8, ex. 7(b)] that, after the ladies are seated at every other chair, the number U_n of ways of seating the men in the ménage problem has asymptotic expansion U_n ~ e^(-2)*n!*(1 + Sum_{k>=1} (-1)^k/(k!(n-1)_k)), where (n)_k = n*(n-1)*...*(n-k+1).
Therefore, it is natural to conjecture that a(n) ~ e^(-2)*n!/(n-2)*(1 + Sum_{k>=1} (-1)^k/(k!(n-1)_k)).

References

  • I. Kaplansky and J. Riordan, The problème des ménages, Scripta Math. 12, (1946), 113-124.
  • J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, chs. 7, 8.

Crossrefs

Programs

  • Mathematica
    a[n_] := If[n<6, 0, Sum[(-1)^k (n-k-1)! Sum[Binomial[8-j, j] Binomial[2n-k+j-10, k-j], {j, Max[k-n+5, 0], Min[k, 4]}], {k, 0, n-1}]];
    Array[a, 24] (* Jean-François Alcover, Sep 19 2018 *)
  • PARI
    a(n) = if (n<=5, 0, sum(k=0, n-1, (-1)^k*(n-k-1)!*sum(j=max(k-n+5, 0), min(k,4), binomial(8-j, j)*binomial(2*n-k+j-10, k-j)))); \\ Michel Marcus, Jun 26 2015

Formula

For n <= 5, a(n)=0; otherwise a(n) = Sum_{0<=k<=n-1}(-1)^k*(n-k-1)! Sum_{max(k-n+5, 0)<=j<=min(k,4)} binomial(8-j, j)*binomial(2*n-k+j-10, k-j).

A059375 Number of seating arrangements for the ménage problem.

Original entry on oeis.org

1, 0, 0, 12, 96, 3120, 115200, 5836320, 382072320, 31488549120, 3191834419200, 390445460697600, 56729732529254400, 9659308746908620800, 1905270127543015833600, 431026303509734220288000, 110865322076320374571008000, 32172949121885378686623744000
Offset: 0

Views

Author

N. J. A. Sloane, Jan 28 2001

Keywords

Comments

The "probleme des menages" asks for the number of gender-alternating seating arrangements for n couples around a circular table with the condition that no two spouses are seated adjacently. - Paul C. Kainen and Michael Somos, Mar 11 2011

Examples

			a(3) = 12 because there is a unique seating arrangement up to circular and clockwise / counterclockwise symmetry. - _Paul C. Kainen_ and _Michael Somos_, Mar 11 2011
		

References

  • L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 184, mu*(n).
  • H. J. Ryser, Combinatorial Mathematics. Mathematical Association of America, Carus Mathematical Monograph 14, 1963, p. 32. equation (2.3).

Crossrefs

Programs

  • Mathematica
    a[0] = 1; a[1] = 0; a[n_] := 4n n! Sum[(-1)^k Binomial[2n-k, k] (n-k)! / (2n-k), {k, 0, n}]; Table[a[n], {n, 0, 17}] (* Jean-François Alcover, Jun 19 2017, from 1st formula *)
  • PARI
    {a(n) = local(A); if( n<3, n==0, A = vector(n); A[3] = 1; for(k=4, n, A[k] = (k * (k - 2) * A[k-1] + k * A[k-2] - 4 * (-1)^k) / (k-2)); 2 * n! * A[n])} /* Michael Somos, Mar 11 2011 */

Formula

a(n) = A000179(n) * 2 * n!.
a(n) = A094047(n) * 2 * n.

A258673 A total of n married couples, including a mathematician M and his wife, are to be seated at the 2n chairs around a circular table, with no man seated next to his wife. After the ladies are seated at every other chair, M is the first man allowed to choose one of the remaining chairs. The sequence gives the number of ways of seating the other men, with no man seated next to his wife, if M chooses the chair that is 11 seats clockwise from his wife's chair.

Original entry on oeis.org

0, 0, 0, 0, 0, 0, 115, 791, 6204, 55004, 543597, 5922929, 70518904, 910711192, 12678337943, 189252400475, 3015217932052, 51067619064756, 916176426421297, 17355904144767765, 346195850534324608, 7252654441500343712, 159210363453691696379, 3654550890669607979359
Offset: 1

Views

Author

Keywords

Comments

This is a variation of the classic ménage problem (cf. A000179).
It is known [Riordan, ch. 8, ex. 7(b)] that, after the ladies are seated at every other chair, the number U_n of ways of seating the men in the ménage problem has asymptotic expansion U_n ~ e^(-2)*n!*(1 + Sum_{k>=1} (-1)^k/(k!(n-1)_k)), where (n)_k = n*(n-1)*...*(n-k+1).
Therefore, it is natural to conjecture that a(n) ~ e^(-2)*n!/(n-2)*(1 + Sum_{k>=1} (-1)^k/(k!(n-1)_k)).
In the general case, M chooses a chair at an odd distance d >= 3 clockwise from his wife. See the corresponding general formula below.

References

  • I. Kaplansky and J. Riordan, The problème des ménages, Scripta Math. 12, (1946), 113-124.
  • J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, chs. 7, 8.

Crossrefs

Programs

  • Mathematica
    a[d_,n_]:=If[n<=#-1,0,Sum[((-1)^k)*(n-k-1)!Sum[Binomial[2#-j-4,j]*Binomial[2(n-#)-k+j+2,k-j],{j,Max[#+k-n-1,0],Min[k,#-2]}],{k,0,n-1}]]&[(d+3)/2];
    Map[a[11,#]&,Range[20]] (* Peter J. C. Moses, Jun 07 2015 *)

Formula

For n <= 6, a(n)=0; otherwise a(n) = Sum_{k=0..n-1} (-1)^k*(n-k-1)! * Sum_{j=max(k-n+6, 0)..min(k,5)} binomial(10-j, j)*binomial(2*n-k+j-12, k-j).
In the general case (see comment), let r=(d+3)/2 and denote the solution by A(r,n). Then A(r,n) is given by the formula
A(r,n)=0 for n <= (d+1)/2; otherwise A(r,n) = Sum_{k=0..n-1} ((-1)^k)*(n-k-1)! * Sum_{j=max(r+k-n-1, 0)..min(k,r-2)} binomial(2r-j-4, j)*binomial(2(n-r) - k + j + 2, k-j).
Note that, if n is even, then 2*Sum_{r=3..(n+2)/2} A(r,n) = A000179(n); if n is odd, then 2*Sum_{r=3..(n+1)/2} A(r,n) + A((n+3)/2, n) = A000179(n).

A259212 A total of n married couples, including a mathematician M and his wife W, are to be seated at the 2n chairs around a circular table. M and W are the first couple allowed to choose chairs, and they choose two chairs next to each other. The sequence gives the number of ways of seating the remaining couples so that women and men are in alternate chairs but M and W are the only couple seated next to each other.

Original entry on oeis.org

0, 0, 0, 6, 72, 1920, 69120, 3402000, 218252160, 17708544000, 1773002649600, 214725759494400, 30941575378560000, 5231894853375590400, 1025881591718766182400, 230901375630648602880000, 59127083048250564931584000, 17091634972762948947148800000
Offset: 1

Views

Author

Vladimir Shevelev, Jun 21 2015

Keywords

Comments

After M and W are seated at neighboring chairs, the problem of enumerating the ways of seating the remaining n-1 married couples is equivalent to the following problem: find the number of ways of seating n-1 married couples at 2*(n-1) chairs in a straight line, men and women in alternate chairs, so that no husband is next to his wife. According to our comment in A000271, this problem has a solution 2*(n-1)!*A000271(n-1), n >= 2. Here the coefficient 2 should be replaced by 1, since the place of the first woman W, by the condition, is already fixed.
Also the number of Hamiltonian paths in the (n-1)-crown graph for n > 3. - Eric W. Weisstein, Mar 27 2018

Crossrefs

Programs

  • Mathematica
    a[n_] := (n-1)! Sum[(-1)^(n-k+1) k! Binomial[n+k-1, 2k], {k, 0, n}]; a[1] = 0; Array[a, 18] (* Jean-François Alcover, Sep 03 2016 *)
    Join[{0}, Table[-(-1)^n (n - 1)! HypergeometricPFQ[{1, 1 - n, n}, {1/2}, 1/4], {n, 2, 20}]] (* Eric W. Weisstein, Mar 27 2018 *)
  • PARI
    a(n) = if (n==1, 0, my(m=n-1); m!*sum(k=0, m, binomial(2*m-k,k)*(m-k)!*(-1)^k)); \\ Michel Marcus, Jun 26 2015

Formula

a(n) = (n-1)!*A000271(n-1), for n > 1.
From Vladimir Shevelev, Jul 07 2015: (Start)
Consider the general formula for solution A(r,n) in A258673 without the restriction A(r,n)=0 for n <= (d+1)/2 in case d=2*n-1. The case when M and W sit at neighboring chairs corresponds to d=1, r=2 or d=2*n-1, r=n+1. In both cases, from this formula we have
A(r,n) = a(n)/(n-1)! = Sum_{j=0..n-1} (-1)^j * binomial(2*n-j-2,j)*(n-j-1)!, n > 1. (End)

Extensions

More terms from Peter J. C. Moses, Jun 21 2015

A332709 Triangle T(n,k) read by rows where T(n,k) is the number of ménage permutations that map 1 to k, with 3 <= k <= n.

Original entry on oeis.org

1, 1, 1, 4, 5, 4, 20, 20, 20, 20, 115, 116, 117, 116, 115, 787, 791, 791, 791, 791, 787, 6184, 6203, 6204, 6205, 6204, 6203, 6184, 54888, 55000, 55004, 55004, 55004, 55004, 55000, 54888, 542805, 543576, 543595, 543596, 543597, 543596, 543595, 543576, 542805
Offset: 3

Views

Author

Peter Kagey, Feb 20 2020

Keywords

Comments

Rows are palindromic.
Conjecture: Rows are unimodal (i.e., increasing, then decreasing).
Conjecture: T(n,k) - T(n,k-1) = A127548(n-2k+4) for n >= 2k - 3. - Peter Kagey, Jan 22 2021

Examples

			Triangle begins:
  n\k|     3      4      5      6      7      8      9     10
  ---+--------------------------------------------------------
   3 |     1
   4 |     1,     1
   5 |     4,     5,     4
   6 |    20,    20,    20,    20
   7 |   115,   116,   117,   116,   115
   8 |   787,   791,   791,   791,   791,   787
   9 |  6184,  6203,  6204,  6205,  6204,  6203,  6184
  10 | 54888, 55000, 55004, 55004, 55004, 55004, 55000, 54888
For n=5 and k=3, the T(5,3)=4 permutations on five letters that start with a 3 are 31524, 34512, 35124, and 35212.
		

Crossrefs

Cf. A127548.
First column given by A258664.
Second column given by A258665.
Third column given by A258666.
Fourth column given by A258667.
Row sums given by A000179.

Programs

  • Mathematica
    T[n_, k_] :=
    Sum[Sum[(-1)^i*(n - i - 1)!*Binomial[2*k - j - 4, j]*
        Binomial[2*(n - k + 1) - i + j, i - j], {j, Max[k + i - n - 1, 0],
         Min[i, k - 2]}], {i, 0, n - 1}]
    (* Peter Kagey, Jan 22 2021 *)

Formula

T(n,k) = Sum_{i=0..n-1} Sum_{j=max(k+i-n-1,0)..min(i,k-2)} (-1)^i*(n-i-1)! * binomial(2k-j-4,j) * binomial(2(n-k+1)-i+j,i-j).
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