A359762 -id:A359762 - cp's OEIS frontend

A047974 a(n) = a(n-1) + 2(n-1)a(n-2).

1, 1, 3, 7, 25, 81, 331, 1303, 5937, 26785, 133651, 669351, 3609673, 19674097, 113525595, 664400311, 4070168161, 25330978113, 163716695587, 1075631907655, 7296866339961, 50322142646161, 356790528924523, 2570964805355607, 18983329135883665, 142389639792952801, 1091556096587136051

Offset: 0

N. J. A. Sloane

nonn

Related to partially ordered sets. - Detlef Pauly (dettodet(AT)yahoo.de), Sep 25 2003
The number of partial permutation matrices P in GL_n with P^2=0. Alternatively, the number of orbits of the Borel group of upper triangular matrices acting by conjugation on the set of matrices M in GL_n with M^2=0. - Brian Rothbach (rothbach(AT)math.berkeley.edu), Apr 16 2004
Number of ways to use the elements of {1..n} once each to form a collection of sequences, each having length 1 or 2. - Bob Proctor, Apr 18 2005
Hankel transform is A108400. - Paul Barry, Feb 11 2008
This is also the number of subsets of equivalent ways to arrange the elements of n pairs, when equivalence is defined under the joint operation of (optional) reversal of elements combined with permutation of the labels and the subset maps to itself. - Ross Drewe, Mar 16 2008
Equals inverse binomial transform of A000898. - Gary W. Adamson, Oct 06 2008
a(n) is also the moment of order n for the measure of density exp(-(x-1)^2/4)/(2*sqrt(Pi)) over the interval -oo..oo. - Groux Roland, Mar 26 2011
The n-th term gives the number of fixed-point-free involutions in S_n^B, the group of permutations on the set {-n,...,-1,1,2,...,n}. - Matt Watson, Jul 26 2012
From Peter Bala, Dec 03 2017: (Start)
a(n+k) == a(n) (mod k) for all n and k. Hence for each k, the sequence a(n) taken modulo k is a periodic sequence and the exact period divides k. Cf. A115329.
More generally, the same divisibility property holds for any sequence with an e.g.f. of the form F(x)*exp(x*G(x)), where F(x) and G(x) are power series with integer coefficients and G(0) = 1. See the Bala link for a proof. (End)

Vincenzo Librandi, Table of n, a(n) for n = 0..200
Peter Alspaugh, James Garrett, Nataša Jonoska, and Masahico Saito, Structures of Monoids Motivated by DNA Origami, arXiv:2501.14966 [math.RA], 2025. See p. 22.
Tewodros Amdeberhan, Valerio De Angelis, Atul Dixit, Victor H. Moll, and Christophe Vignat, From sequences to polynomials and back, via operator orderings, J. Math. Phys. 54, 123502 (2013); Alternative copy
Peter Bala, Integer sequences that become periodic on reduction modulo k for all k
Jonathan Burns, Assembly Graph Words - Single Transverse Component (Counts); Alternative copy
Jonathan Burns, Egor Dolzhenko, Natasa Jonoska, Tilahun Muche and Masahico Saito, Four-Regular Graphs with Rigid Vertices Associated to DNA Recombination, Discrete Applied Mathematics, Volume 161, Issues 10-11, July 2013, Pages 1378-1394; Alternative copy.
Jonathan Burns and Tilahun Muche, Counting Irreducible Double Occurrence Words, arXiv preprint arXiv:1105.2926 [math.CO], 2011.
Samuele Giraudo, Combalgebraic structures on decorated cliques, arXiv:1709.08416 [math.CO], 2017; and also, Formal Power Series and Algebraic Combinatorics, Séminaire Lotharingien de Combinatoire, 78B.15, 2017, p. 8.
Tom Halverson and Mike Reeks, Gelfand Models for Diagram Algebras, arXiv preprint arXiv:1302.6150 [math.RT], 2013.
Andrei Khruzin, Enumeration of chord diagrams, arXiv:math/0008209 [math.CO], 2000.
G. Latouche and P. G. Taylor, A stochastic fluid model for an ad hoc mobile network, Queueing Syst. 63, No. 1-4, 109-129 (2009), eq. (1).
Robert A. Proctor, Let's Expand Rota's Twelvefold Way for Counting Partitions!, arXiv:math/0606404 [math.CO], 2006-2007.
Jocelyn Quaintance and Harris Kwong, Permutations and combinations of colored multisets, JIS 13 (2010) #10.2.6.
Index entries for related partition-counting sequences
Index entries for sequences related to Hermite polynomials

Row sums of A067147.
Column k=2 of A359762.
Cf. A000085, A000680, A000898, A001147, A001813, A100861, A108400, A115329, A132101.
Sequences with e.g.f = exp(x + q*x^2): A158968 (q=-9), A158954 (q=-4), A362177 (q=-3), A362176 (q=-2), A293604 (q=-1), A000012 (q=0), this sequence (q=1), A115329 (q=2), A293720 (q=4).

N = 18; A = zeros(N,1); for n = 1:N; a = factorial(n); s = 0; k = 0; while k <= floor(n/2); b = factorial(n - 2*k); c = factorial(k); s = s + a/(b*c); k = k+1; end; A(n) = s; end; disp(A); % Ross Drewe, Mar 16 2008

[n le 2 select 1 else Self(n-1) + 2*(n-2)*Self(n-2): n in [1..40]]; // G. C. Greubel, Jul 12 2024

seq( add(n!/((n-2*k)!*k!), k=0..floor(n/2)), n=0..30 ); # Detlef Pauly (dettodet(AT)yahoo.de), Nov 15 2001
with(combstruct):seq(count(([S,{S=Set(Union(Z,Prod(Z,Z)))},labeled],size=n)),n=0..30); # Detlef Pauly (dettodet(AT)yahoo.de), Sep 25 2003
A047974 := n -> I^(-n)*orthopoly[H](n, I/2):
seq(A047974(n), n=0..26); # Peter Luschny, Nov 29 2017

Range[0, 23]!*CoefficientList[ Series[ Exp[x*(1-x^2)/(1 - x)], {x, 0,23 }], x] - (* Zerinvary Lajos, Mar 23 2007 *)
Table[I^(-n)*HermiteH[n, I/2], {n, 0, 23}] - (* Alyssa Byrnes and C. Vignat, Jan 31 2013 *)

my(x='x+O('x^66)); Vec(serlaplace(exp(x^2+x))) \\ Joerg Arndt, May 04 2013

[(-i)^n*hermite(n,i/2) for n in range(41)] # G. C. Greubel, Jul 12 2024

E.g.f.: exp(x^2+x). - Len Smiley, Dec 11 2001
Binomial transform of A001813 (with interpolated zeros). - Paul Barry, May 09 2003
a(n) = Sum_{k=0..n} C(k,n-k)*n!/k!. - Paul Barry, Mar 29 2007
a(n) = Sum_{k=0..floor(n/2)} C(n,2k)*(2k)!/k!; - Paul Barry, Feb 11 2008
G.f.: 1/(1-x-2*x^2/(1-x-4*x^2/(1-x-6*x^2/(1-x-8*x^2/(1-... (continued fraction). -Paul Barry, Apr 10 2009
E.g.f.: Q(0); Q(k) = 1+(x^2+x)/(2*k+1-(x^2+x)*(2*k+1)/((x^2+x)+(2*k+2)/Q(k+1))); (continued fraction). - Sergei N. Gladkovskii, Nov 24 2011
a(n) = D^n(exp(x)) evaluated at x = 0, where D is the operator sqrt(1+4*x)*d/dx. Cf. A000085 and A115329. - Peter Bala, Dec 07 2011
a(n) ~ 2^(n/2 - 1/2)*exp(sqrt(n/2) - n/2 - 1/8)*n^(n/2). - Vaclav Kotesovec, Oct 08 2012
E.g.f.: 1 + x*(E(0)-1)/(x+1) where E(k) = 1 + (1+x)/(k+1)/(1-x/(x+1/E(k+1) )); (continued fraction). - Sergei N. Gladkovskii, Jan 26 2013
a(n) = i^(-n)*H_{n}(i/2) with i the imaginary unit and H_{n} the Hermite polynomial of degree n. - Alyssa Byrnes and C. Vignat, Jan 31 2013
E.g.f.: -Q(0)/x where Q(k) = 1 - (1+x)/(1 - x/(x - (k+1)/Q(k+1) )); (continued fraction). - Sergei N. Gladkovskii, Mar 06 2013
G.f.: 1/Q(0), where Q(k) = 1 + x*2*k - x/(1 - x*(2*k+2)/Q(k+1)); (continued fraction). - Sergei N. Gladkovskii, Apr 17 2013
E.g.f.: E(0)-1-x-x^2, where E(k) = 2 + 2*x*(1+x) - 8*k^2 + x^2*(1+x)^2*(2*k+3)*(2*k-1)/E(k+1); (continued fraction). - Sergei N. Gladkovskii, Dec 21 2013
E.g.f.: Product_{k>=1} 1/(1 + (-x)^k)^(mu(k)/k). - Ilya Gutkovskiy, May 26 2019
a(n) = Sum_{k=0..floor(n/2)} 2^k*B(n, k), where B are the Bessel numbers A100861. - Peter Luschny, Jun 04 2021

A115329 Expansion of e.g.f.: exp(x + 2*x^2).

Original entry on oeis.org

1, 1, 5, 13, 73, 281, 1741, 8485, 57233, 328753, 2389141, 15539261, 120661465, 866545993, 7140942173, 55667517781, 484124048161, 4046845186145, 36967280461093, 328340133863533, 3137853448906601, 29405064157989241

Offset: 0

Paul D. Hanna, Jan 20 2006

Term-by-term square of sequence with e.g.f.: exp(x+m/2*x^2) is given by e.g.f.: exp(x/(1-m*x))/sqrt(1-m^2*x^2) for all m.
Combinatorial interpretation: a(n) counts the partitions of a set of n distinguishable objects into subsets of size 1 and 2 with the additional feature that the constituents of the subset of size 2 acquire 2 colors. - Karol A. Penson and P. Blasiak (blasiak(AT)lptl.jussieu.fr), Jun 03 2006
In general, e.g.f. exp(x+m*x^2) has general term sum{k=0..n, C(n,k)*m^k*(n-k)!/(n-m*k)!}. [Paul Barry, Nov 07 2008]
The sequence terms have the form 4*m + 1 (follows from the recurrence). a(n+k) = a(n) (mod k) holds for all n and k by an induction argument making use of the recurrence equation. For each k the sequence a(n) taken modulo k is thus periodic with exact period dividing k. - Peter Bala, Nov 15 2017

Seiichi Manyama, Table of n, a(n) for n = 0..665 (terms 0..200 from Vincenzo Librandi)
Magdalena Boos, Giovanni Cerulli Irelli, Francesco Esposito, Parabolic orbits of 2-nilpotent elements for classical groups, arXiv:1802.06425 [math.RT], 2018.

Column k=4 of A359762.
Cf. A000085, A047974, A115330.
Sequences with e.g.f = exp(x + q*x^2): A158968 (q=-9), A158954 (q=-4), A362177 (q=-3), A362176 (q=-2), A293604 (q=-1), A000012 (q=0), A047974 (q=1), this sequence (q=2), A293720 (q=4).

R:=PowerSeriesRing(Rationals(), 30);
Coefficients(R!(Laplace( Exp(x+2*x^2) ))); // G. C. Greubel, Jul 12 2024

a := n -> I^(1 - n)*2^((3*(n - 1))/2)*KummerU((1 - n)/2, 3/2, -1/8):
seq(simplify(a(n)), n=0..21); # Peter Luschny, Nov 21 2017

Range[0, 20]! CoefficientList[Series[Exp[(x + 2 x^2)], {x, 0, 20}], x] (* Vincenzo Librandi, May 22 2013 *)

a(n)=local(m=4);n!*polcoeff(exp(x+m/2*x^2+x*O(x^n)),n)

[(-i*sqrt(2))^n*hermite(n, i/(2*sqrt(2))) for n in range(31)] # G. C. Greubel, Jul 12 2024

Term-by-term square equals A115330 which has e.g.f.: exp(x/(1-4*x))/sqrt(1-16*x^2).
a(n) = Sum_{k=0..floor(n/2)} C(n-k,k)2^k*n!/(n-k)! = Sum_{k=0..n} C(n,k)2^k*(n-k)!/(n-2k)!. - Paul Barry, Nov 07 2008
a(n) = D^n(exp(x)) evaluated at x = 0, where D is the operator sqrt(1+8*x)*d/dx. Cf. A000085 and A047974. - Peter Bala, Dec 07 2011
a(n) = a(n-1) + 4*(n-1)*a(n-2). - R. J. Mathar, Dec 10 2011
a(n) ~ 2^(n-1/2)*exp(sqrt(n)/2-n/2-1/16)*n^(n/2). - Vaclav Kotesovec, Oct 19 2012
G.f.: 1/Q(0), where Q(k)= 1 + 4*x*k - x/(1 - 4*x*(k+1)/Q(k+1)); (continued fraction). - Sergei N. Gladkovskii, Apr 17 2013
G.f.: 1/G(0), where G(k)= 1 - x - 4*(k+1)*x^2/G(k+1); (continued fraction). - Sergei N. Gladkovskii, Jul 21 2013
a(n) = i^(1 - n)*2^(3*(n - 1)/2)*KummerU((1 - n)/2, 3/2, -1/8). - Peter Luschny, Nov 21 2017
a(n) = (-i*sqrt(2))^n * Hermite(n, i/(2*sqrt(2))). - G. C. Greubel, Jul 12 2024

More terms from Karol A. Penson and P. Blasiak (blasiak(AT)lptl.jussieu.fr), Jun 03 2006

A277614 a(n) is the coefficient of x^n/n! in exp(x + n*x^2/2).

Original entry on oeis.org

1, 1, 3, 10, 73, 426, 4951, 41308, 658785, 7149628, 144963451, 1937124696, 47660873833, 756536698360, 21888570052623, 402400189738576, 13384439813823361, 279666289640774928, 10512823691028429235, 246061359639756047008, 10314843348672697017801, 267328220273408530004896, 12363686002049118477390343, 351473836594567725961268160, 17776996370247936310502612833, 550002942283550733215994429376

Offset: 0

Paul D. Hanna, Nov 10 2016

nonn

From Peter Luschny, Jan 17 2023: (Start)
a(n) is the number of connection patterns in a telephone system with n possibilities of connection and n subscribers.
The number of matchings of a complete multigraph K(n, n).
The main diagonal of A359762. (End)
Let k be a positive integer. It appears that reducing this sequence modulo k produces an eventually periodic sequence. For example, modulo 10 the sequence becomes [1, 3, 0, 3, 6, 1, 8, 5, 8, 1, 6, 3, 0, 3, 6, 1, 8, 5, 8, 1, 6, 3, 0, 3, 6, ...], with an apparent period [1, 8, 5, 8, 1, 6, 3, 0, 3, 6] of length 10 starting at a(5). - Peter Bala, Apr 16 2023

			E.g.f.: A(x) = 1 + x + 3*x^2/2! + 10*x^3/3! + 73*x^4/4! + 426*x^5/5! + 4951*x^6/6! + 41308*x^7/7! + 658785*x^8/8! + 7149628*x^9/9! + 144963451*x^10/10! + ...
The table of coefficients of x^k/k! in exp(x + n*x^2/2) begins:
n=0: 1, 1,  1,  1,   1,    1,     1,      1,       1, ...;
n=1: 1, 1,  2,  4,  10,   26,    76,    232,     764, ...;
n=2: 1, 1,  3,  7,  25,   81,   331,   1303,    5937, ...;
n=3: 1, 1,  4, 10,  46,  166,   856,   3844,   21820, ...;
n=4: 1, 1,  5, 13,  73,  281,  1741,   8485,   57233, ...;
n=5: 1, 1,  6, 16, 106,  426,  3076,  15856,  123516, ...;
n=6: 1, 1,  7, 19, 145,  601,  4951,  26587,  234529, ...;
n=7: 1, 1,  8, 22, 190,  806,  7456,  41308,  406652, ...;
n=8: 1, 1,  9, 25, 241, 1041, 10681,  60649,  658785, ...;
n=9: 1, 1, 10, 28, 298, 1306, 14716,  85240, 1012348, ...;
n=10:1, 1, 11, 31, 361, 1601, 19651, 115711, 1491281, ...; ...
in which the main diagonal forms this sequence.
In the above table, the e.g.f. of the m-th diagonal equals the e.g.f. of this sequence multiplied by ( LambertW(-x^2)/(-x^2) )^(m/2).
Example,
A(x)*sqrt(-LambertW(-x^2))/x = 1 + x + 4*x^2/2! + 13*x^3/3! + 106*x^4/4! + 601*x^5/5! + 7456*x^6/6! + 60649*x^7/7! + 1012348*x^8/8! + ...
equals the e.g.f. of the next lower diagonal in the table.
RELATED SERIES.
-LambertW(-x^2) = x^2 + 2*x^4/2! + 3^2*x^6/3! + 4^3*x^8/4! + 5^4*x^10/5! + 6^5*x^12/6! + ... + n^(n-1)*x^(2*n)/n! + ...
sqrt(-LambertW(-x^2)) = x + 3^0*x^3/(1!*2) + 5*x^5/(2!*2^2) + 7^2*x^7/(3!*2^3) + 9^3*x^9/(4!*2^4) + ... + (2*n+1)^(n-1)*x^(2*n+1)/(n!*2^n) + ...

Seiichi Manyama, Table of n, a(n) for n = 0..416
Urszula Bednarz and Małgorzata Wołowiec-Musiał, On a new generalization of telephone numbers, Turkish Journal of Mathematics: Vol. 43: No. 3, (2019).

Cf. A359762, A362300, A362314, A362319.

a := n -> add(binomial(n, j) * doublefactorial(j-1) * n^(j/2), j = 0..n, 2):
seq(a(n), n = 0..25); # Peter Luschny, Jan 17 2023

{a(n) = n!*polcoeff( exp(x + n*x^2/2 + x*O(x^n)),n)}
for(n=0,30,print1(a(n),", "))

from math import factorial, comb
def oddfactorial(n: int) -> int:
    return factorial(2 * n) // (2**n * factorial(n))
def a(n: int) -> int:
    return sum(comb(n, 2*j) * oddfactorial(j) * n**j for j in range(n+1))
print([a(n) for n in range(26)]) # Peter Luschny, Jan 17 2023

E.g.f.: exp( sqrt(-LambertW(-x^2)) ) / (1 + LambertW(-x^2)).
a(n) ~ (exp(1) + (-1)^n*exp(-1)) * n^n / (sqrt(2) * exp(n/2)). - Vaclav Kotesovec, Nov 11 2016
a(n) = Sum_{j=0..n, j even} binomial(n, j) * (j - 1)!! * n^(j/2). - Peter Luschny, Jan 17 2023

A293720 Expansion of e.g.f.: exp(x + 4*x^2).

Original entry on oeis.org

1, 1, 9, 25, 241, 1041, 10681, 60649, 658785, 4540321, 51972841, 415198521, 4988808529, 44847866545, 563683953561, 5586645006601, 73228719433921, 788319280278849, 10747425123292105, 124265401483446361, 1757874020223846321, 21640338257575264081

Offset: 0

Seiichi Manyama, Oct 15 2017

nonn

Seiichi Manyama, Table of n, a(n) for n = 0..612

Column k=2 of A293724.
Column k=8 of A359762.
Sequences with e.g.f = exp(x + q*x^2): A158968 (q=-9), A158954 (q=-4), A362177 (q=-3), A362176 (q=-2), A293604 (q=-1), A000012 (q=0), A047974 (q=1), A115329 (q=2), this sequence (q=4).

R:=PowerSeriesRing(Rationals(), 30);
Coefficients(R!(Laplace( Exp(x+4*x^2) ))); // G. C. Greubel, Jul 12 2024

CoefficientList[Series[E^(x + 4*x^2), {x,0,30}], x] * Range[0,30]! (* Vaclav Kotesovec, Oct 15 2017 *)

my(N=66, x='x+O('x^N)); Vec(serlaplace(exp(x+4*x^2)))

[(-2*i)^n*hermite(n, i/4) for n in range(31)] # G. C. Greubel, Jul 12 2024

a(n) ~ 2^((3*n-1)/2) * exp(-1/32 + sqrt(2*n)/4 - n/2) * n^(n/2). - Vaclav Kotesovec, Oct 15 2017

a(n) = (-2*i)^n * Hermite(n, i/4). - G. C. Greubel, Jul 12 2024

A362277 Square array T(n,k), n >= 0, k >= 0, read by antidiagonals downwards, where T(n,k) = n! * Sum_{j=0..floor(n/2)} (-k/2)^j * binomial(n-j,j)/(n-j)!.

Original entry on oeis.org

1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, -1, -2, 1, 1, 1, -2, -5, -2, 1, 1, 1, -3, -8, 1, 6, 1, 1, 1, -4, -11, 10, 41, 16, 1, 1, 1, -5, -14, 25, 106, 31, -20, 1, 1, 1, -6, -17, 46, 201, -44, -461, -132, 1, 1, 1, -7, -20, 73, 326, -299, -1952, -895, 28, 1, 1, 1, -8, -23, 106, 481, -824, -5123, -1028, 6481, 1216, 1

Offset: 0

Seiichi Manyama, Apr 13 2023

			Square array begins:
  1,  1,  1,   1,    1,    1,     1, ...
  1,  1,  1,   1,    1,    1,     1, ...
  1,  0, -1,  -2,   -3,   -4,    -5, ...
  1, -2, -5,  -8,  -11,  -14,   -17, ...
  1, -2,  1,  10,   25,   46,    73, ...
  1,  6, 41, 106,  201,  326,   481, ...
  1, 16, 31, -44, -299, -824, -1709, ...

Seiichi Manyama, Antidiagonals n = 0..139, flattened

Columns k=0..6 give A000012, (-1)^n * A001464(n), A293604, A362278, A362176, A362279, A362177.
Main diagonal gives A362276.
T(n,2*n) gives A362282.
Cf. A359762, A362302.

T(n,k) = n!*sum(j=0,n\2, (-k/2)^j/(j!*(n-2*j)!));

E.g.f. of column k: exp(x - k*x^2/2).
T(n,k) = T(n-1,k) - k*(n-1)*T(n-2,k) for n > 1.
T(n,k) = n! * Sum_{j=0..floor(n/2)} (-k/2)^j / (j! * (n-2*j)!).

A115327 E.g.f.: exp(x + 3/2*x^2).

Original entry on oeis.org

1, 1, 4, 10, 46, 166, 856, 3844, 21820, 114076, 703216, 4125496, 27331624, 175849480, 1241782816, 8627460976, 64507687696, 478625814544, 3768517887040, 29614311872416, 244419831433696, 2021278543778656, 17419727924101504

Offset: 0

Paul D. Hanna, Jan 20 2006

nonn

Term-by-term square of sequence with e.g.f.: exp(x+m/2*x^2) is given by e.g.f.: exp(x/(1-m*x))/sqrt(1-m^2*x^2) for all m.

a(n) is also the number of square roots of any permutation in S_{3n} whose disjoint cycle decomposition consists of n cycles of length 3. - Luis Manuel Rivera Martínez, Feb 26 2015

Vincenzo Librandi, Table of n, a(n) for n = 0..200
John Campbell, A class of symmetric difference-closed sets related to commuting involutions, Discrete Mathematics & Theoretical Computer Science, Vol 19 no. 1, 2017.
Jesús Leaños, Rutilo Moreno, and Luis Manuel Rivera-Martínez, On the number of mth roots of permutations, arXiv:1005.1531 [math.CO], 2010-2011.
Jesús Leaños, Rutilo Moreno, and Luis Manuel Rivera-Martínez, On the number of mth roots of permutations, Australas. J. Combin. 52 (2012), 41-54, (Theorems 1 and 2).

Column k=3 of A359762.

Cf. A115328.

Range[0, 20]! CoefficientList[Series[Exp[(x + 3 / 2 x^2)], {x, 0, 20}], x] (* Vincenzo Librandi, May 22 2013 *)

a(n)=local(m=3);n!*polcoeff(exp(x+m/2*x^2+x*O(x^n)),n)

Term-by-term square equals A115328 which has e.g.f.: exp(x/(1-3*x))/sqrt(1-9*x^2).
From Paul Barry, Apr 10 2009: (Start)
G.f.: 1/(1-x-3*x^2/(1-x-6*x^2/(1-x-9*x^2/(1-x-12*x^2/(1-... (continued fraction);
a(n) = a(n-1)+3*(n-1)*a(n-2). (End)
a(n) ~ exp(sqrt(n/3)-n/2-1/12)*3^(n/2)*n^(n/2)/sqrt(2). - Vaclav Kotesovec, Oct 19 2012
G.f.: 1/Q(0), where Q(k)= 1 + 3*x*k - x/(1 - 3*x*(k+1)/Q(k+1)); (continued fraction). - Sergei N. Gladkovskii, Apr 17 2013
a(n) = n!*Sum_{k=0..floor(n/2)}3^k/(2^k*k!*(n-2*k)!). - Luis Manuel Rivera Martínez, Feb 26 2015

A362043 Square array T(n,k), n >= 0, k >= 0, read by antidiagonals downwards, where T(n,k) = n! * Sum_{j=0..floor(n/3)} (k/6)^j * binomial(n-2j,j)/(n-2j)!.

Original entry on oeis.org

1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 3, 5, 1, 1, 1, 1, 4, 9, 11, 1, 1, 1, 1, 5, 13, 21, 31, 1, 1, 1, 1, 6, 17, 31, 81, 106, 1, 1, 1, 1, 7, 21, 41, 151, 351, 337, 1, 1, 1, 1, 8, 25, 51, 241, 736, 1233, 1205, 1, 1, 1, 1, 9, 29, 61, 351, 1261, 2689, 5769, 5021, 1

Offset: 0

Seiichi Manyama, Apr 15 2023

			Square array begins:
  1,  1,  1,   1,   1,   1,   1, ...
  1,  1,  1,   1,   1,   1,   1, ...
  1,  1,  1,   1,   1,   1,   1, ...
  1,  2,  3,   4,   5,   6,   7, ...
  1,  5,  9,  13,  17,  21,  25, ...
  1, 11, 21,  31,  41,  51,  61, ...
  1, 31, 81, 151, 241, 351, 481, ...

Seiichi Manyama, Antidiagonals n = 0..139, flattened

Columns k=0..2 give A000012, A190865, A001470.
Main diagonal gives A362173.
T(n,2*n) gives A362300.
T(n,6*n) gives A362301.
Cf. A359762, A362302.

T(n, k) = n!*sum(j=0, n\3, (k/6)^j/(j!*(n-3*j)!));

E.g.f. of column k: exp(x + k*x^3/6).
T(n,k) = T(n-1,k) + k * binomial(n-1,2) * T(n-3,k) for n > 2.
T(n,k) = n! * Sum_{j=0..floor(n/3)} (k/6)^j / (j! * (n-3*j)!).

A376826 Array read by antidiagonals: T(n,k) = n! * [x^n] exp(2x + (k/2)x^2), n >= 0, k >= 0.

Original entry on oeis.org

1, 1, 2, 1, 2, 4, 1, 2, 5, 8, 1, 2, 6, 14, 16, 1, 2, 7, 20, 43, 32, 1, 2, 8, 26, 76, 142, 64, 1, 2, 9, 32, 115, 312, 499, 128, 1, 2, 10, 38, 160, 542, 1384, 1850, 256, 1, 2, 11, 44, 211, 832, 2809, 6512, 7193, 512, 1, 2, 12, 50, 268, 1182, 4864, 15374, 32400, 29186, 1024

Offset: 0

Andrew Howroyd, Oct 07 2024

			Array begins:
======================================================
n\k |   0    1    2     3     4     5     6      7 ...
----+-------------------------------------------------
  0 |   1    1    1     1     1     1     1      1 ...
  1 |   2    2    2     2     2     2     2      2 ...
  2 |   4    5    6     7     8     9    10     11 ...
  3 |   8   14   20    26    32    38    44     50 ...
  4 |  16   43   76   115   160   211   268    331 ...
  5 |  32  142  312   542   832  1182  1592   2062 ...
  6 |  64  499 1384  2809  4864  7639 11224  15709 ...
  7 | 128 1850 6512 15374 29696 50738 79760 118022 ...
     ...

Andrew Howroyd, Table of n, a(n) for n = 0..1325 (first 51 antidiagonals)
Arvind Ayyer, Hiranya Kishore Dey and Digjoy Paul, How large is the character degree sum compared to the character table sum for a finite group?, arXiv preprint arXiv:2406.06036, [math.RT], 2024.

Columns 0..5 are A000079, A005425, A000898, A202830, A193778, A202832.

Cf. A359762, A373625.

T(n,k) = {sum(i=0, n\2, binomial(n,2*i) * 2^(n-2*i) * k^i * (2*i)!/(2^i*i!))}

E.g.f. of column k: exp(2*x + k*x^2/2).
Column k is the binomial transform of column k of A359762.
T(n,k) = Sum_{i=0..floor(n/2)} binomial(n,2*i) * 2^(n-2*i) * k^i * (2*i-1)!!.
T(n,k) = Sum_{i=0..floor(n/2)} 2^(n-3*i) * k^i * n! / ((n-2*i)! * i!).

A115331 E.g.f.: exp(x+5/2*x^2).

Original entry on oeis.org

1, 1, 6, 16, 106, 426, 3076, 15856, 123516, 757756, 6315976, 44203776, 391582456, 3043809016, 28496668656, 241563299776, 2378813448976, 21703877431056, 223903020594016, 2177251989389056, 23448038945820576, 241173237884726176

Offset: 0

Paul D. Hanna, Jan 20 2006

nonn

Term-by-term square of sequence with e.g.f.: exp(x+m/2*x^2) is given by e.g.f.: exp(x/(1-m*x))/sqrt(1-m^2*x^2) for all m.

a(n) is also the number of square roots of any permutation in S_{5n} whose disjoint cycle decomposition consists of n cycles of length 5. - Luis Manuel Rivera Martínez, Feb 26 2015

Vincenzo Librandi, Table of n, a(n) for n = 0..200
Jesús Leaños, Rutilo Moreno, and Luis Manuel Rivera-Martínez, On the number of mth roots of permutations, arXiv:1005.1531 [math.CO], 2010-2011.
Jesús Leaños, Rutilo Moreno, and Luis Manuel Rivera-Martínez, On the number of mth roots of permutations , Australas. J. Combin. 52 (2012), 41-54 (Theorems 1 and 2).

Column k=5 of A359762.

Cf. A115332.

Range[0, 20]! CoefficientList[Series[Exp[(x + 5 / 2 x^2)], {x, 0, 20}], x] (* Vincenzo Librandi, May 22 2013 *)

a(n)=local(m=5);n!*polcoeff(exp(x+m/2*x^2+x*O(x^n)),n)

Term-by-term square equals A115332 which has e.g.f.: exp(x/(1-5*x))/sqrt(1-25*x^2).
a(n) ~ exp(sqrt(n/5)-n/2-1/20)*5^(n/2)*n^(n/2)/sqrt(2). - Vaclav Kotesovec, Oct 19 2012
a(n) = n!*Sum_{k=0..floor(n/2)}5^k/(2^k*k!*(n-2*k)!). - Luis Manuel Rivera Martínez, Feb 26 2015
O.g.f.: 1/(1-x - 5*x^2/(1-x - 10*x^2/(1-x - 15*x^2/(1-x - 20*x^2/(1-x - 25*x^2/(1-x -...)))))), a continued fraction (after Paul Barry in A115327). - Paul D. Hanna, Mar 08 2015

cp's OEIS Frontend

A047974 a(n) = a(n-1) + 2*(n-1)*a(n-2).

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A115329 Expansion of e.g.f.: exp(x + 2*x^2).

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A277614 a(n) is the coefficient of x^n/n! in exp(x + n*x^2/2).

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A293720 Expansion of e.g.f.: exp(x + 4*x^2).

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A362277 Square array T(n,k), n >= 0, k >= 0, read by antidiagonals downwards, where T(n,k) = n! * Sum_{j=0..floor(n/2)} (-k/2)^j * binomial(n-j,j)/(n-j)!.

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A115327 E.g.f.: exp(x + 3/2*x^2).

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A362043 Square array T(n,k), n >= 0, k >= 0, read by antidiagonals downwards, where T(n,k) = n! * Sum_{j=0..floor(n/3)} (k/6)^j * binomial(n-2*j,j)/(n-2*j)!.

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A047974 a(n) = a(n-1) + 2(n-1)a(n-2).

A362043 Square array T(n,k), n >= 0, k >= 0, read by antidiagonals downwards, where T(n,k) = n! * Sum_{j=0..floor(n/3)} (k/6)^j * binomial(n-2j,j)/(n-2j)!.

A376826 Array read by antidiagonals: T(n,k) = n! * [x^n] exp(2x + (k/2)x^2), n >= 0, k >= 0.