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 1-3 of 3 results.

A002119 Bessel polynomial y_n(-2).

Original entry on oeis.org

1, -1, 7, -71, 1001, -18089, 398959, -10391023, 312129649, -10622799089, 403978495031, -16977719590391, 781379079653017, -39085931702241241, 2111421691000680031, -122501544009741683039, 7597207150294985028449, -501538173463478753560673
Offset: 0

Views

Author

N. J. A. Sloane

Keywords

Comments

Absolute values give denominators of successive convergents to e using continued fraction 1+2/(1+1/(6+1/(10+1/(14+1/(18+1/(22+1/26...)))))).
Absolute values give number of different arrangements of nonnegative integers on a set of n 6-sided dice such that the dice can add to any integer from 0 to 6^n-1. For example when n=2, there are 7 arrangements that can result in any total from 0 to 35. Cf. A273013. The number of sides on the dice only needs to be the product of two distinct primes, of which 6 is the first example. - Elliott Line, Jun 10 2016
Absolute values give number of Krasner factorizations of (x^(6^n)-1)/(x-1) into n polynomials p_i(x), i=1,2,...,n, satisfying p_i(1)=6. In these expressions 6 can be replaced with any product of two distinct primes (Krasner and Ranulac, 1937). - William P. Orrick, Jan 18 2023
Absolute values give number of pairs (s, b) where s is a covering of the 1 X 2n grid with 1 X 2 dimers and equal numbers of red and blue 1 X 1 monomers and b is a bijection between the red monomers and the blue monomers that does not map adjacent monomers to each other. Ilya Gutkovskiy's formula counts such pairs by an inclusion-exclusion argument. The correspondence with Elliott Line's dice problem is that a dimer corresponds to a die containing an arithmetic progression of length 6 and a pair (r, b(r)), where r is a red monomer and b(r) its image under b, corresponds to a die containing the sum of an arithmetic progression of length 2 and an arithmetic progression of length 3. - William P. Orrick, Jan 19 2023

Examples

			Example from _William P. Orrick_, Jan 19 2023: (Start)
For n=2 the Bessel polynomial is y_2(x) = 1 + 3x + 3x^2 which satisfies y_2(-2) = -7.
The |a(2)|=7 dice pairs are
  {{0,1,2,3,4,5}, {0,6,12,18,24,30}},
  {{0,1,2,18,19,20}, {0,3,6,9,12,15}},
  {{0,1,2,9,10,11}, {0,3,6,18,21,24}},
  {{0,1,6,7,12,13}, {0,2,4,18,20,22}},
  {{0,1,12,13,24,25}, {0,2,4,6,8,10}},
  {{0,1,2,6,7,8}, {0,3,12,15,24,27}},
  {{0,1,4,5,8,9}, {0,2,12,14,24,26}}.
The corresponding Krasner factorizations of (x^36-1)/(x-1) are
  {(x^6-1)/(x-1), (x^36-1)/(x^6-1)},
  {((x^36-1)/(x^18-1))*((x^3-1)/(x-1)), (x^18-1)/(x^3-1)},
  {((x^18-1)/(x^9-1))*((x^3-1)/(x-1)), ((x^36-1)/(x^18-1))*((x^9-1)/(x^3-1))},
  {((x^18-1)/(x^6-1))*((x^2-1)/(x-1)), ((x^36-1)/(x^18-1))*((x^6-1)/(x^2-1))},
  {((x^36-1)/(x^12-1))*((x^2-1)/(x-1)), (x^12-1)/(x^2-1)},
  {((x^12-1)/(x^6-1))*((x^3-1)/(x-1)), ((x^36-1)/(x^12-1))*((x^6-1)/(x^3-1))},
  {((x^12-1)/(x^4-1))*((x^2-1)/(x-1)), ((x^36-1)/(x^12-1))*((x^4-1)/(x^2-1))}.
The corresponding monomer-dimer configurations, with dimers, red monomers, and blue monomers represented by the symbols '=', 'R', and 'B', and bijections between red and blue monomers given as sets of ordered pairs, are
  (==, {}),
  (B=R, {(3,1)}),
  (BBRR, {(3,1),(4,2)}),
  (RBBR, {(1,3),(4,2)}),
  (R=B, {(1,3)}),
  (BRRB, {(2,4),(3,1)}),
  (RRBB, {(1,3),(2,4)}).
(End)

References

  • L. Euler, 1737.
  • J. Riordan, Combinatorial Identities, Wiley, 1968, p. 77.
  • 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).

Links

Crossrefs

Cf. A053556, A053557, A001514, A065920, A065921, A065922, A065707, A000806, A006199, A065923.
See also A033815.
Numerators of the convergents of e are A001517, which has a similar interpretation to a(n) in terms of monomer-dimer configurations, but omitting the restriction that adjacent monomers not be mapped to each other by the bijection.
Polynomial coefficients are in A001498.

Programs

  • Maple
    f:=proc(n) option remember; if n <= 1 then 1 else f(n-2)+(4*n-2)*f(n-1); fi; end;
[seq(f(n), n=0..20)]; # This is for the unsigned version. - N. J. A. Sloane, May 09 2016
seq(simplify((-1)^n*KummerU(-n, -2*n, -1)), n = 0..17); # Peter Luschny, May 10 2022
  • Mathematica
    Table[(-1)^k (2k)! Hypergeometric1F1[-k, -2k, -1]/k!, {k, 0, 10}] (* Vladimir Reshetnikov, Feb 16 2011 *)
nxt[{n_,a_,b_}]:={n+1,b,a-2b(2n+1)}; NestList[nxt,{1,1,-1},20][[All,2]] (* Harvey P. Dale, Aug 18 2017 *)
  • PARI
    {a(n)= if(n<0, n=-n-1); sum(k=0, n, (2*n-k)!/ (k!*(n-k)!)* (-1)^(n-k) )} /* Michael Somos, Apr 02 2007 */
  • PARI
    {a(n)= local(A); if(n<0, n= -n-1); A= sqrt(1 +4*x +x*O(x^n)); n!*polcoeff( exp((A-1)/2)/A, n)} /* Michael Somos, Apr 02 2007 */
  • PARI
    {a(n)= local(A); if(n<0, n= -n-1); n+=2 ; for(k= 1, n, A+= x*O(x^k); A= truncate( (1+x)* exp(A) -1-A) ); A+= x*O(x^n); A-= A^2; -(-1)^n*n!* polcoeff( serreverse(A), n)} /* Michael Somos, Apr 02 2007 */
  • Sage
    A002119 = lambda n: hypergeometric([-n, n+1], [], 1)
[simplify(A002119(n)) for n in (0..17)] # Peter Luschny, Oct 17 2014

Formula

D-finite with recurrence a(n) = -2(2n-1)*a(n-1) + a(n-2). - T. D. Noe, Oct 26 2006
If y = x + Sum_{k>=2} A005363(k)*x^k/k!, then y = x + Sum_{k>=2} a(k-2)(-y)^k/k!. - Michael Somos, Apr 02 2007
a(-n-1) = a(n). - Michael Somos, Apr 02 2007
a(n) = (1/n!)*Integral_{x>=-1} (-x*(1+x))^n*exp(-(1+x)). - Paul Barry, Apr 19 2010
G.f.: 1/Q(0), where Q(k) = 1 - x + 2*x*(k+1)/Q(k+1); (continued fraction). - Sergei N. Gladkovskii, May 17 2013
Expansion of exp(x) in powers of y = x*(1 + x): exp(x) = 1 + y - y^2/2! + 7*y^3/3! - 71*y^4/4! + 1001*y^5/5! - .... E.g.f.: (1/sqrt(4*x + 1))*exp(sqrt(4*x + 1)/2 - 1/2) = 1 - x + 7*x^2/2! - 71*x^3/3! + .... - Peter Bala, Dec 15 2013
a(n) = hypergeom([-n, n+1], [], 1). - Peter Luschny, Oct 17 2014
a(n) = sqrt(Pi/exp(1)) * BesselI(1/2+n, 1/2) + (-1)^n * BesselK(1/2+n, 1/2) / sqrt(exp(1)*Pi). - Vaclav Kotesovec, Jul 22 2015
a(n) ~ (-1)^n * 2^(2*n+1/2) * n^n / exp(n+1/2). - Vaclav Kotesovec, Jul 22 2015
From G. C. Greubel, Aug 16 2017: (Start)
G.f.: (1/(1-t))*hypergeometric2f0(1, 1/2; -; -4*t/(1-t)^2).
E.g.f.: (1+4*t)^(-1/2) * exp((sqrt(1+4*t) - 1)/2). (End)
a(n) = Sum_{k=0..n} (-1)^k*binomial(n,k)*binomial(n+k,k)*k!. - Ilya Gutkovskiy, Nov 24 2017
a(n) = (-1)^n*KummerU(-n, -2*n, -1). - Peter Luschny, May 10 2022

Extensions

More terms from Vladeta Jovovic, Apr 03 2000

A079267 d(n,s) = number of perfect matchings on {1, 2, ..., n} with s short pairs.

Original entry on oeis.org

1, 0, 1, 1, 1, 1, 5, 6, 3, 1, 36, 41, 21, 6, 1, 329, 365, 185, 55, 10, 1, 3655, 3984, 2010, 610, 120, 15, 1, 47844, 51499, 25914, 7980, 1645, 231, 21, 1, 721315, 769159, 386407, 120274, 25585, 3850, 406, 28, 1, 12310199, 13031514, 6539679, 2052309, 446544, 70371, 8106, 666, 36, 1
Offset: 0

Views

Author

Jeremy Martin (martin(AT)math.umn.edu), Feb 05 2003

Keywords

Comments

Read backwards, the n-th row of the triangle gives the Hilbert series of the variety of slopes determined by n points in the plane.
From Paul Barry, Nov 25 2009: (Start)
Reversal of coefficient array for the polynomials P(n,x) = Sum_{k=0..n} (C(n+k,2k)*(2k)!/(2^k*k!))*x^k*(1-x)^(n-k).
Note that P(n,x) = Sum_{k=0..n} A001498(n,k)*x^k*(1-x)^(n-k). (End)
Equivalent to the original definition: Triangle of fixed-point free involutions on [1..2n] (=A001147) by number of cycles with adjacent integers. - Olivier Gérard, Mar 23 2011
Conjecture: Asymptotically, the n-th row has a Poisson distribution with mean 1. - David Callan, Nov 11 2012
This is also the number of configurations of n indistinguishable pairs placed on the vertices of the ladder graph P_1 X P_2n (i.e., a path of length 2n) such that s such pairs are joined by an edge; equivalently the number of "s-domino" configurations in the game of memory played on a 1 X 2n rectangular array, see [Young]. - Donovan Young, Oct 23 2018

Examples

			Triangle begins:
   1
   0  1
   1  1  1
   5  6  3 1
  36 41 21 6 1
From _Paul Barry_, Nov 25 2009: (Start)
Production matrix begins
       0,      1,
       1,      1,      1,
       4,      4,      2,     1,
      18,     18,      9,     3,     1,
      96,     96,     48,    16,     4,    1,
     600,    600,    300,   100,    25,    5,   1,
    4320,   4320,   2160,   720,   180,   36,   6,  1,
   35280,  35280,  17640,  5880,  1470,  294,  49,  7, 1,
  322560, 322560, 161280, 53760, 13440, 2688, 448, 64, 8, 1
Complete this by adding top row (1,0,0,0,...) and take inverse: we obtain
   1,
   0,  1,
  -1, -1,  1,
  -2, -2, -2,  1,
  -3, -3, -3, -3,  1,
  -4, -4, -4, -4, -4,  1,
  -5, -5, -5, -5, -5, -5,  1,
  -6, -6, -6, -6, -6, -6, -6,  1,
  -7, -7, -7, -7, -7, -7, -7, -7,  1,
  -8, -8, -8, -8, -8, -8, -8, -8, -8,  1 (End)
The 6 involutions with no fixed point on [1..6] with only one 2-cycle with adjacent integers are ((1, 2), (3, 5), (4, 6)), ((1, 3), (2, 4), (5, 6)), ((1, 3), (2, 6), (4, 5)), ((1, 5), (2, 3), (4, 6)), ((1, 5), (2, 6), (3, 4)), and ((1, 6), (2, 5), (3, 4)).

References

  • G. Kreweras and Y. Poupard, Sur les partitions en paires d'un ensemble fini totalement ordonné, Publications de l'Institut de Statistique de l'Université de Paris, 23 (1978), 57-74.

Links

Crossrefs

Columns are A278990, A000806, A006198, A006199, A006200.
Row sums are A001147.
d(2n,n) gives A365744.

Programs

  • Maple
    d := (n,s) -> 1/s! * sum('((-1)^(h-s)*(2*n-h)!/(2^(n-h)*(n-h)!*(h-s)!))','h'=s..n):
# alternative by R. J. Mathar, Aug 19 2022
A079267 := proc(n,k)
    option remember ;
    if n =0 and k =0 then
        1;
    elif k > n or k < 0 then
        0;
    else
        procname(n-1,k-1)+(2*n-2-k)*procname(n-1,k)+(k+1)*procname(n-1,k+1) ;
    end if;
end proc:
seq(seq( A079267(n,k),k=0..n),n=0..13) ;
  • Mathematica
    nmax = 9; d[n_, s_] := (2^(s-n)*(2n-s)!* Hypergeometric1F1[s-n, s-2n, -2])/ (s!*(n-s)!); Flatten[ Table[d[n, s], {n, 0, nmax}, {s, 0, n}]] (* Jean-François Alcover, Oct 19 2011, after Maple *)
  • PARI
    {T(n, k) = 2^(k-n)*binomial(n,k)*hyperu(k-n, k-2*n, -2)};
for(n=0,10, for(k=0,n, print1(round(T(n,k)), ", "))) \\ G. C. Greubel, Apr 10 2019
  • Sage
    [[2^(k-n)*binomial(n,k)*hypergeometric_U(k-n,k-2*n,-2).simplify_hypergeometric() for k in (0..n)] for n in (0..10)] # G. C. Greubel, Apr 10 2019

Formula

d(n, s) = (1/s!) * Sum_{h=s..n} (((-1)^(h-s)*(2*n-h)!/(2^(n-h)*(n-h)!*(h-s)!))).
E.g.f.: exp((x-1)*(1-sqrt(1-2*y)))/sqrt(1-2*y). - Vladeta Jovovic, Dec 15 2008

Extensions

Extra terms added by Paul Barry, Nov 25 2009

A065707 Bessel polynomial {y_n}'(-2).

Original entry on oeis.org

0, 1, -9, 126, -2270, 49995, -1301139, 39066076, -1329148764, 50536328085, -2123542798685, 97722882268506, -4887863677728954, 264025383760041631, -15317578742680490535, 949914821498248213560, -62707584375936061905464, 4390358319593012839913001
Offset: 0

Views

Author

N. J. A. Sloane, Dec 08 2001

Keywords

References

  • J. Riordan, Combinatorial Identities, Wiley, 1968, p. 77.

Links

Crossrefs

Cf. A001514, A065920, A065921, A065922, A065707, A006199.

Programs

  • Mathematica
    Join[{0}, Table[2*n*Pochhammer[1/2, n]*(-4)^(n - 1)*Hypergeometric1F1[1 - n, -2*n, -1], {n, 1, 50}]] (* G. C. Greubel, Aug 14 2017 *)
  • PARI
    for(n=0,50, print1(sum(k=0,n-1, (n+k+1)!/(2*(n-k-1)!*k!)), ", ")) \\ G. C. Greubel, Aug 14 2017

Formula

From G. C. Greubel, Aug 14 2017: (Start)
a(n) = 2*n*(1/2)_{n}*(-4)^(n - 1)* hypergeometric1f1(1 - n, -2*n, -1).
E.g.f.: ((1 + 4*x)^(3/2) - 2*x*(1 + 4*x)^(1/2) - 1)* exp((sqrt(1 + 4*x) -1)/2)/(4*(1 + 4*x)^(3/2)). (End)
G.f.: (x/(1-x)^3)*hypergeometric2f0(2,3/2; - ; -4*x/(1-x)^2). - G. C. Greubel, Aug 16 2017
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Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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