A001044 -id:A001044 - cp's OEIS frontend

A204579 Triangle read by rows: matrix inverse of the central factorial numbers T(2n, 2k) (A036969).

1, -1, 1, 4, -5, 1, -36, 49, -14, 1, 576, -820, 273, -30, 1, -14400, 21076, -7645, 1023, -55, 1, 518400, -773136, 296296, -44473, 3003, -91, 1, -25401600, 38402064, -15291640, 2475473, -191620, 7462, -140, 1, 1625702400, -2483133696, 1017067024, -173721912, 14739153, -669188, 16422, -204, 1

Offset: 1

M. F. Hasler, Feb 03 2012

This is a signed version of A008955 with rows in reverse order. - Peter Luschny, Feb 04 2012

			Triangle starts:
  [1]         1;
  [2]        -1,        1;
  [3]         4,       -5,         1;
  [4]       -36,       49,       -14,       1;
  [5]       576,     -820,       273,     -30,       1;
  [6]    -14400,    21076,     -7645,    1023,     -55,    1;
  [7]    518400,  -773136,    296296,  -44473,    3003,  -91,    1;
  [8] -25401600, 38402064, -15291640, 2475473, -191620, 7462, -140, 1;

José L. Cereceda, Sums of powers of integers and the sequence A304330, arXiv:2405.05268 [math.GM], 2024. See p. 6.
Mark W. Coffey and Matthew C. Lettington, On Fibonacci Polynomial Expressions for Sums of mth Powers, their implications for Faulhaber's Formula and some Theorems of Fermat, arXiv:1510.05402 [math.NT], 2015.

Cf. A036969, A008955, A008275, A121408, A001044 (column 1), A101686 (alternating row sums), A234324 (central terms).

# From Peter Luschny, Feb 29 2024: (Start)
ogf := n -> local j; z^2*mul(z^2 - j^2, j = 1..n-1):
Trow := n -> local k; seq(coeff(expand(ogf(n)), z, 2*k), k = 1..n):
# Alternative:
f := w -> (w^sqrt(t) + w^(-sqrt(t)))/2: egf := f((x/2 + sqrt(1 + (x/2)^2))^2):
ser := series(egf, x, 20): cx := n -> coeff(ser, x, 2*n):
Trow := n -> local k; seq((2*n)!*coeff(cx(n), t, k), k = 1..n):  # (End)
# Assuming offset 0:
rowpoly := n -> (-1)^n * pochhammer(1 - sqrt(x), n) * pochhammer(1 + sqrt(x), n):
row := n -> local k; seq(coeff(expand(rowpoly(n)), x, k), k = 0..n):
seq(print(row(n)), n = 0..7);  # Peter Luschny, Aug 03 2024

rows = 10;
t[n_, k_] := 2*Sum[j^(2*n)*(-1)^(k - j)/((k - j)!*(k + j)!), {j, 1, k}];
T = Table[t[n, k], {n, 1, rows}, {k, 1, rows}] // Inverse;
Table[T[[n, k]], {n, 1, rows}, {k, 1, n}] // Flatten (* Jean-François Alcover, Jul 14 2018 *)

select(concat(Vec(matrix(10,10,n,k,T(n,k)/*from A036969*/)~^-1)), x->x)

def A204579(n, k): return (-1)^(n-k)*A008955(n, n-k)
for n in (0..7): print([A204579(n, k) for k in (0..n)]) # Peter Luschny, Feb 05 2012

T(n, k) = (-1)^(n-k)*A008955(n, n-k). - Peter Luschny, Feb 05 2012
T(n, k) = Sum_{i=k-n..n-k} (-1)^(n-k+i)*s(n,k+i)*s(n,k-i) = Sum_{i=0..2*k} (-1)^(n+i)*s(n,i)*s(n,2*k-i), where s(n,k) are Stirling numbers of the first kind, A048994. - Mircea Merca, Apr 07 2012
From Peter Bala, Aug 29 2012: (Start)
T(n, k) = T(n-1, k-1) - (n-1)^2*T(n-1, k). (Recurrence equation.)
Let E(x) = cosh(sqrt(2*x)) = Sum_{n >= 0} x^n/{(2*n)!/2^n} and
L(x) = 2*{arcsinh(sqrt(x/2))}^2 = Sum_{n >=1} (-1)^n*(n-1)!^2*x^n/{(2*n)!/2^n}.
L(x) is the compositional inverse of E(x) - 1.
A generating function for the triangle is E(t*L(x)) = 1 + t*x + t*(-1 + t)*x^2/6 + t*(4 - 5*t + t^2)*x^3/90 + ..., where the sequence of denominators [1,1,6,90,...] is given by (2*n)!/2^n. Cf. A008275 with generating function exp(t*log(1+x)).
The e.g.f. is E(t*L(x^2/2)) = cosh(2*sqrt(t)*arcsinh(x/2)) = 1 + t*x^2/2! + t*(t-1)*x^4/4! + t*(t-1)*(t-4)*x^6/6! + .... (End)
From Peter Luschny, Feb 29 2024: (Start)
T(n, k) = [z^(2*k)] z^2*Product_{j=1..n-1} (z^2 - j^2).
T(n, k) = (2*n)! * [t^k] [x^(2*n)] (w^sqrt(t) + w^(-sqrt(t)))/2 where w = (x/2 + sqrt(1 + (x/2)^2))^2. (End)
T(n, k) = [x^k] (-1)^n * Pochhammer(1 - sqrt(x), n) * Pochhammer(1 + sqrt(x), n), assuming offset 0. - Peter Luschny, Aug 03 2024
Integral_{0..oo} x^s / (cosh(x))^(2*n) dx = (2^(2*n - s - 1) * s! * (-1)^(n-1)) / (2*n - 1)!)*Sum_{k=1..n} T(n,k)*DirichletEta(s - 2*k + 2). - Ammar Khatab, Apr 11 2025

Typo in data corrected by Peter Luschny, Feb 05 2012

A221976 The number of n X n matrices with zero determinant and with entries a permutation of [1,2,..,n^2].

Original entry on oeis.org

0, 0, 2736, 8290316160

Offset: 1

R. J. Mathar, May 12 2013

This counts a subset of all (n^2)! = A088020(n) matrices which contain elements which are a permutation of [n^2]. The range of determinants is characterized in A085000, and the size of the set of different determinants in A088217.

Because any combination of row and column permutation of matrices with distinct elements generates (n!)^2 = A001044(n) different matrices, and because these restricted permutations leave the (absolute value of) the determinant constant, a(n) is a multiple of A001044(n). This factor does not yet take into account that matrix transpositions also maintain the values of determinants (and which never can be achieved by row or column permutation).

a(n) = A136609(n)*A001044(n).

A239836 Number of ordered pairs of permutation functions f,g on a size n set where f(g(g(x))) = g(f(f(x))).

Original entry on oeis.org

1, 1, 2, 6, 48, 360, 2880, 20160, 241920, 3265920, 47174400, 678585600, 12933043200, 193037644800, 3661488230400, 74537438976000, 1736591560704000, 36991492521984000

Offset: 0

Chad Brewbaker, Mar 27 2014

Cf. A000012, A000085, A000142, A088311, A053529, A001044, A239779, A255525.

a(n) = A255525(n) * n!.

a(8)-a(9) from Giovanni Resta, Mar 27 2014

a(10)-a(16) from Max Alekseyev, Jan 29 2025

A350824 Triangle read by rows: T(n,k) is the number of patterns of length n with all distinct run lengths and maximum value k, n >= 0, k = 0..floor(sqrt(8*n+1)-1/2).

Original entry on oeis.org

1, 0, 1, 0, 1, 0, 1, 4, 0, 1, 4, 0, 1, 8, 0, 1, 20, 36, 0, 1, 24, 36, 0, 1, 36, 72, 0, 1, 52, 108, 0, 1, 112, 576, 576, 0, 1, 128, 612, 576, 0, 1, 200, 1116, 1152, 0, 1, 264, 1584, 1728, 0, 1, 384, 2520, 2880, 0, 1, 700, 8064, 20736, 14400, 0, 1, 868, 9432, 22464, 14400

Offset: 0

Andrew Howroyd, Feb 12 2022

			Triangle begins:
  1;
  0, 1;
  0, 1;
  0, 1,   4;
  0, 1,   4;
  0, 1,   8;
  0, 1,  20,   36;
  0, 1,  24,   36;
  0, 1,  36,   72;
  0, 1,  52,  108;
  0, 1, 112,  576,  576;
  0, 1, 128,  612,  576;
  0, 1, 200, 1116, 1152;
  ...
The T(5,1) = 1 pattern is 11111.
The T(5,2) = 8 patterns are 12222, 11222, 11122, 11112, 21111, 22111, 22211, 22221.

Andrew Howroyd, Table of n, a(n) for n = 0..958 (rows 0..100)

Row sums are A351292.

Cf. A000217, A001044, A003056, A008289, A351637, A351640.

P(n) = {Vec(-1 + prod(k=1, n, 1 + y*x^k + O(x*x^n)))}
R(u, k) = {k*[subst(serlaplace(p)/y, y, k-1) | p<-u]}
T(n)={my(u=P(n), v=concat([1], sum(k=1, n, R(u, k)*sum(r=k, n, y^r*binomial(r, k)*(-1)^(r-k)) ))); [Vecrev(p) | p<-v]}
{ my(A=T(16)); for(n=1, #A, print(A[n])) }

T(n,k) = Sum_{j=1..k} R(n,j)*binomial(k, j)*(-1)^(k-j) for n > 0, where R(n,k) = Sum_{j=1..A003056(n)} k*(k-1)^(j-1) * j! * A008289(n,j).
T(n,k) = k! * A351637(n,k).
T(A000217(n),n) = A001044(n). - Alois P. Heinz, Feb 15 2022

A027451 First diagonal of A027447.

Original entry on oeis.org

1, 1, 4, 9, 144, 100, 3600, 11025, 78400, 63504, 6350400, 5336100, 768398400, 662547600, 577152576, 2029052025, 519437318400, 463325262400, 150117385017600, 135480939978384, 122885206329600, 111967718990400, 54192375991353600, 49770428644836900

Offset: 1

Olivier Gérard

nonn

Equals the denominators of MN(z;n)/(n!)^2 for n =>1, see A162990. - Johannes W. Meijer, Jul 21 2009

It appears that a(n) = denominator of n^2*sum(1/k^2,k=1..n). - Gary Detlefs, May 29 2010

From Johannes W. Meijer, Jul 21 2009: (Start)
Equals A002944(n)^2.
Equals A001044(n-1)/A025527(n)^2.
(End)

a[n_] := (LCM @@ Range[n]/n)^2; Table[a[n], {n, 1, 20}] (* Jean-François Alcover, Mar 05 2013, after Johannes W. Meijer *)

Numerators of sequence a[ n, n ] in (a[ i, j ])^3 where a[ i, j ] = 1/i if j<=i, 0 if j>i.

a(n) = (lcm($1..n)/n)^2. - Johannes W. Meijer, Jul 21 2009

More terms from Sean A. Irvine, Nov 04 2019

A061692 Triangle of generalized Stirling numbers.

Original entry on oeis.org

1, 1, 4, 1, 27, 36, 1, 172, 864, 576, 1, 1125, 17500, 36000, 14400, 1, 7591, 351000, 1746000, 1944000, 518400, 1, 52479, 7197169, 80262000, 191394000, 133358400, 25401600, 1, 369580, 151633440, 3691514176, 17188416000, 23866214400, 11379916800, 1625702400

Offset: 1

N. J. A. Sloane, Jun 19 2001

			1; 1,4; 1,27,36; 1,172,864,576; ...

Alois P. Heinz, Rows n = 1..100, flattened
J.-M. Sixdeniers, K. A. Penson and A. I. Solomon, Extended Bell and Stirling Numbers From Hypergeometric Exponentiation, J. Integer Seqs. Vol. 4 (2001), #01.1.4.

Diagonals give A001044, A061695, A061693, A061694. Cf. A061691.

Row sums give A061684.

b:= proc(n) option remember; expand(
      `if`(n=0, 1, add(x*b(n-i)/i!^3, i=1..n)))
    end:
T:= n-> (p-> seq(coeff(p, x, i)/i!, i=1..n))(b(n)*n!^3):
seq(T(n), n=1..10);  # Alois P. Heinz, Sep 10 2019

R[0, ] = 1; R[n, x_] := R[n, x] = x*Sum[Binomial[n, k]^2*Binomial[n-1, k]*R[k, x], {k, 0, n-1}]; Table[CoefficientList[R[n, x], x] // Rest, {n, 1, 8}] // Flatten (* Jean-François Alcover, Sep 01 2015, after Peter Bala *)

T(n, k) = 1/k!*Sum multinomial(n, n_1, n_2, ..n_k)^3, where the sum extends over all compositions (n_1, n_2, .., n_k) of n into exactly k nonnegative parts. - Vladeta Jovovic, Apr 23 2003

The row polynomials R(n,x) satisfy the recurrence equation R(n,x) = x*( sum {k = 0..n-1} binomial(n,k)^2*binomial(n-1,k)*R(k,x) ) with R(0,x) = 1. Also R(n,x + y) = sum {k = 0..n} binomial(n,k)^3*R(k,x)*R(n-k,y). - Peter Bala, Sep 17 2013

More terms from Vladeta Jovovic, Apr 23 2003

A134373 a(n) = ((2n)!)^3.

Original entry on oeis.org

1, 8, 13824, 373248000, 65548320768000, 47784725839872000000, 109903340320478724096000000, 662559760549147780765974528000000, 9159226129831418921308831875072000000000, 262435789155225791087396177124997988352000000000

Offset: 0

Artur Jasinski, Oct 22 2007

nonn

Christian Elsholtz, Golomb’s Conjecture on Prime Gaps, arXiv:1604.06903 [math.NT], 2016.
Christian Elsholtz, Golomb’s Conjecture on Prime Gaps, The American Mathematical Monthly 124.4 (2017): 365-368.

Cf. A000142, A001044, A000442, A036740, A010050, A134366, A134367, A134368, A134369, A134371, A134373, A134374, A134375.

Table[((2n)!)^(3), {n, 0, 10}]
((2*Range[0, 10])!)^3 (* Harvey P. Dale, Jul 25 2016 *)

[factorial(2*n)**3 for n in range(0,9)] # Stefano Spezia, Apr 22 2025

Definition corrected by Harvey P. Dale, Jul 25 2016

A136301 Frequency of occurrence for each possible "probability of derangement" for a Secret Santa drawing in which each person draws a name in sequence and the only person who does not draw someone else's name is the one who draws the final name.

Original entry on oeis.org

1, 1, 1, 1, 5, 2, 1, 1, 13, 6, 13, 2, 6, 2, 1, 1, 29, 14, 73, 6, 42, 18, 29, 2, 18, 8, 14, 2, 6, 2, 1, 1, 61, 30, 301, 14, 186, 86, 301, 6, 102, 48, 186, 18, 102, 42, 61, 2, 42, 20, 86, 8, 48, 20, 30, 2, 18, 8, 14, 2, 6, 2, 1, 1, 125, 62, 1081, 30, 690, 330, 2069, 14, 414, 200, 1394

Offset: 3

Brian Parsonnet, Mar 22 2008

The sequence is best represented as a series of columns 1..n, where each column j has 2^(j-1) rows (see Example). For more details, see A136300.

The first column represents the case for 3 people (offset 3).

			Represented as a series of columns, where column j has 2^(j-1) rows, the sequence begins:
  row |j = 1   2   3   4   5 ...
  ----+-------------------------
    1 |    1   1   1   1   1 ...
    2 |        1   5  13  29 ...
    3 |        2   6  14  30 ...
    4 |        1  13  73 301 ...
    5 |            2   6  14 ...
    6 |            6  42 186 ...
    7 |            2  18  86 ...
    8 |            1  29 301 ...
    9 |                2   6 ...
   10 |               18 102 ...
   11 |                8  48 ...
   12 |               14 186 ...
   13 |                2  18 ...
   14 |                6 102 ...
   15 |                2  42 ...
   16 |                1  61 ...
   17 |                    2 ...
  ... |                  ... ...
.
If there are 5 people, numbered 1-5 according to the order in which they draw a name, and person #5 draws name #5, the first four people must draw 1-4 as a proper derangement, and there are 9 ways of doing so: 21435 / 23415 / 24135 / 31425 / 34125 / 34215 / 41235 / 43125 / 43215.
But the probability of each derangement depends on how many choices exist at each successive draw. The first person can draw from 4 possibilities (2,3,4,5). The second person nominally has 3 to choose from, unless the first person drew number 2, in which case person 2 may draw 4 possibilities (1,3,4,5), and so on. The probabilities of 21435 and 24135 are both then
        1/4 * 1/4 * 1/2 * 1/2 = 1/64.
More generally, if there are n people, at the i-th turn (i = 1..n), person i has either (n-i) or (n-i+1) choices, depending on whether the name of the person who is drawing has been chosen yet. A way to represent the two cases above is 01010, where a 0 indicates that the person's number is not yet drawn, and a 1 indicates it is.
For the n-th person to be forced to choose his or her own name, the last digit of this pattern must be 0, by definition. Similarly, the 1st digit must be a 0, and the second to last digit must be a 1. So all the problem patterns start with 0 and end with 10. For 5 people, that leaves 4 target patterns which cover all 9 derangements. By enumeration, that distribution can be shown to be (for the 3rd column = 5 person case):
        0-00-10 1 occurrences
        0-01-10 5 occurrences
        0-10-10 2 occurrences
        0-11-11 1 occurrences
1;
1, 1;
1, 5, 2, 1;
1, 13, 6, 13, 2, 6, 2, 1;
1, 29, 14, 73, 6, 42, 18, 29, 2, 18, 8, 14, 2, 6, 2, 1;

Brian Parsonnet, Table of n, a(n) for n = 3..257
Brian Parsonnet, Probability of Derangements

The application of this table towards final determination of the probabilities of derangements leads to sequence A136300, which is the sequence of numerators. The denominators are in A001044.
A048144 represents the peak value of all odd-numbers columns.
A000255 equals the sum of the bottom half of each column.
A000166 equals the sum of each column.
A047920 represents the frequency of replacements by person drawing at position n.
A008277, Triangle of Stirling numbers of 2nd kind, can be derived from A136301 through a series of transformations (see "Probability of Derangements.pdf").
Cf. A371761.

maxP = 15;
rows = Range[1, 2^(nP = maxP - 3)];
pasc = Table[
   Binomial[p + 1, i] - If[i >= p, 1, 0], {p, nP}, {i, 0, p}];
sFreq = Table[0, {maxP - 1}, {2^nP}]; sFreq[[2 ;; maxP - 1, 1]] = 1;
For[p = 1, p <= nP, p++,
  For[s = 1, s <= p, s++, rS = Range[2^(s - 1) + 1, 2^s];
        sFreq[[p + 2, rS]] = pasc[[p + 1 - s, 1 ;; p + 2 - s]] .
            sFreq[[s ;; p + 1, 1 ;; 2^(s - 1)]]]];
TableForm[ Transpose[ sFreq ] ]
(* Code snippet to illustrate the conjectured connection with A371761: *)
R[n_] := Table[Transpose[sFreq][[2^n]][[r]], {r, n + 1, maxP - 1}]
For[n = 0, n <= 6, n++, Print[n + 1, ": ", R[n]]] (* Peter Luschny, Apr 10 2024 *)

H(r,c) = Sum_{j=0..c-L(r)-1} H(T(r), L(r)+j) * M(c-T(r)-1, j) where M(y,z) = binomial distribution (y,z) when y - 1 > z and (y,z)-1 when y-1 <= z and T(r) = A053645 and L(r) = A000523.

Conjecture: Assume the table represented as in the Example section. Then row 2^n is row n + 1 of A371761. - Peter Luschny, Apr 10 2024

Edited by Brian Parsonnet, Mar 01 2011

A136609 (1/(n!)^2) * number of ways to arrange the consecutive numbers 1...n^2 in an n X n matrix with determinant = 0.

Original entry on oeis.org

0, 0, 76, 14392910

Offset: 1

Hugo Pfoertner, Jan 21 2008

The computation of a(5) seems to be currently (Jan 2008) out of reach (compare with A088021(5)).

			a(1)=0 because det((1))/=0, a(2)=0, because the only possible determinants of a matrix with elements {1,2,3,4} are +-2, +-5 and +-10.

Cf. A001044, A046747, a(3)=A088215(0), a(4)=A136608(0), A221976.

A192722 T(n,k) = Sum of multinomial(n; n_1,n_2,...,n_k)^2, where the sum extends over all compositions (n_1,n_2,...,n_k) of n into exactly k nonnegative parts.

Original entry on oeis.org

1, 1, 4, 1, 18, 36, 1, 68, 432, 576, 1, 250, 3900, 14400, 14400, 1, 922, 32400, 252000, 648000, 518400, 1, 3430, 262542, 3880800, 19404000, 38102400, 25401600, 1, 12868, 2119152, 56664384, 493920000, 1795046400, 2844979200, 1625702400

Offset: 1

Peter Bala, Jul 11 2011

Compare with triangle A019538, whose entries are given by
... Sum multinomial(n; n_1,n_2,...,n_k), where the sum extends over all compositions (n_1,n_2,...,n_k) of n into exactly k nonnegative parts.
For related tables see A061691 and A192721.
Let P be the poset of all ordered pairs (S,T) of subsets of [n] with |S|=|T|, ordered componentwise by inclusion.  T(n,k) is the number of length k chains in P from ({},{}) to ([n],[n]). - Geoffrey Critzer, Apr 15 2020

			The triangle begins
n/k|..1.....2.......3........4........5........6
================================================
.1.|..1
.2.|..1.....4
.3.|..1....18.....36
.4.|..1....68.....432......576
.5.|..1...250....3900....14400....14400
.6.|..1...922...32400...252000...648000...518400
...
T(4,2) = 68:
There are 3 compositions of 4 into 2 parts, namely, 4 = 2 + 2 = 1 + 3 = 3 + 1; hence
T(4,2) = (4!/(2!*2!))^2 + (4!/(1!*3!))^2 + (4!/(3!*1!))^2
= 36 + 16 + 16 = 68.
Matrix identity: A192721 * Pascal's triangle = row reverse of A192722:
/...1................\ /..1..............\
|...3.....1...........||..1....1..........|
|..19....16.....5.....||..1....2....1.....|
|.211...299....65....1||..1....3....3....1|
|.....................||..................|
=
/...1...................\
|...4......1.............|
|..36.....18......1......|
|.576....432.....68.....1|
|........................|

Alois P. Heinz, Rows n = 1..100, flattened

Cf. A001044, A002190, A061691, A192721, A102221 (row sums), A000275 (alternating row sums).

J := unapply(BesselJ(0, 2*sqrt(-1)*sqrt(z)), z):
G := 1/(1-x*(J(z)-1)):
Gser := simplify(series(G, z = 0, 15)):
for n from 1 to 14 do
P[n] := n!^2*sort(coeff(Gser, z, n)) od:
for n from 1 to 14 do seq(coeff(P[n], x, k), k = 1..n) od;
# yields sequence in triangular form
# second Maple program:
b:= proc(n) option remember; expand(
      `if`(n=0, 1, add(x*b(n-i)/i!^2, i=1..n)))
    end:
T:= n-> (p-> seq(coeff(p, x, i), i=1..n))(b(n)*n!^2):
seq(T(n), n=1..14);  # Alois P. Heinz, Sep 10 2019

b[n_] := b[n] = Expand[If[n == 0, 1, Sum[x b[n-i]/i!^2, {i, 1, n}]]];
T[n_] := Function[p, Table[Coefficient[p, x, i], {i, 1, n}]][b[n] n!^2];
Table[T[n], {n, 1, 14}] // Flatten (* Jean-François Alcover, Dec 07 2019, after Alois P. Heinz *)

Generating function: Let J(z) = Sum_{n>=0} z^n/n!^2. Then
1 + Sum_{n>=1} (Sum_{k = 1..n} T(n,k)*x^k)*z^n/n!^2 = 1/(1 - x*(J(z) - 1))
  = 1 + x*z + (x + 4*x^2)*z^2/2!^2 + (x + 18*x^2 + 36*x^3)*z^3/3!^2 + ....
Relations with other sequences:
The change of variable z -> z/x followed by x -> 1/(x - 1) transforms the above bivariate generating function 1/(1 - x*(J(z) - 1)) into (1 - x)/(-x + J(z*(x-1))), which is the generating function for A192721.
1/k!*T(n,k) = A061691(n,k).
T(n,n) = n!^2 = A001044(n).
Row sums = A102221.
For n>=1, Sum_{k = 1..n} (-1)^(n+k)*T(n,k)/k = A002190(n).

cp's OEIS Frontend

A204579 Triangle read by rows: matrix inverse of the central factorial numbers T(2*n, 2*k) (A036969).

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A221976 The number of n X n matrices with zero determinant and with entries a permutation of [1,2,..,n^2].

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A239836 Number of ordered pairs of permutation functions f,g on a size n set where f(g(g(x))) = g(f(f(x))).

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A350824 Triangle read by rows: T(n,k) is the number of patterns of length n with all distinct run lengths and maximum value k, n >= 0, k = 0..floor(sqrt(8*n+1)-1/2).

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PARI

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A027451 First diagonal of A027447.

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Mathematica

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A061692 Triangle of generalized Stirling numbers.

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Maple

Mathematica

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A134373 a(n) = ((2n)!)^3.

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Mathematica

Sage

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A136301 Frequency of occurrence for each possible "probability of derangement" for a Secret Santa drawing in which each person draws a name in sequence and the only person who does not draw someone else's name is the one who draws the final name.

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A204579 Triangle read by rows: matrix inverse of the central factorial numbers T(2n, 2k) (A036969).