login
This site is supported by donations to The OEIS Foundation.

 

Logo

Annual Appeal: Today, Nov 11 2014, is the 4th anniversary of the launch of the new OEIS web site. 70,000 sequences have been added in these four years, all edited by volunteers. Please make a donation (tax deductible in the US) to help keep the OEIS running.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A082137 Square array of transforms of binomial coefficients, read by antidiagonals. 13
1, 1, 1, 1, 2, 2, 1, 3, 6, 4, 1, 4, 12, 16, 8, 1, 5, 20, 40, 40, 16, 1, 6, 30, 80, 120, 96, 32, 1, 7, 42, 140, 280, 336, 224, 64, 1, 8, 56, 224, 560, 896, 896, 512, 128, 1, 9, 72, 336, 1008, 2016, 2688, 2304, 1152, 256, 1, 10, 90, 480, 1680, 4032, 6720, 7680, 5760, 2560, 512 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

0,5

COMMENTS

Rows are associated with the expansions of (x^k/k!)exp(x)cosh(x) (leading zeros dropped). Rows include A011782, A057711, A080929, A082138, A080951, A082139, A082140, A082141. Columns are of the form 2^(k-1)C(n+k, k). Diagonals include A092246, A082143, A082144, A082145, A069720.

T(n, k) is also the number of idempotent order-preserving and order-decreasing partial transformations (of an n-chain) of width k (width(alpha)= |Dom(alpha)|). - Abdullahi Umar, Oct 02 2008

Read as a triangle this is A119468 with rows reversed. A119468 has e.g.f. exp(z*x)/(1-tanh(x)). - Peter Luschny, Aug 01 2012

Read as a triangle this is a subtriangle of A198793. - Philippe Deléham, Nov 10 2013

LINKS

Table of n, a(n) for n=0..65.

Laradji, A. and Umar, A. Combinatorial results for semigroups of order-preserving partial transformations, Journal of Algebra 278, (2004), 342-359.

Laradji, A. and Umar, A. Combinatorial results for semigroups of order-decreasing partial transformations, J. Integer Seq. 7 (2004), 04.3.8

FORMULA

Square array defined by T(n, k)=(2^(n-1)+0^n/2)C(n + k, n)= Sum{k=0..n, C(n+k, k+j)C(k+j, k)(1+(-1)^j)/2 }.

As an infinite lower triangular matrix, equals A007318 * A134309. - Gary W. Adamson, Oct 19 2007

O.g.f. for array read as a triangle: (1-x*(1+t))/((1-x)*(1-x*(1+2*t))) = 1 + x*(1+t) + x^2*(1+2*t+2*t^2) + x^3*(1+3*t+6*t^2+4*t^3) + .... - Peter Bala, Apr 26 2012

For array read as a triangle: T(n,k) = 2*T(n-1,k) + 2*T(n-1,k-1) - T(n-2,k) -2*T(n-2,k-1), T(0,0) = T(1,0) = T(1,1) = 1, T(n,k) = 0 if k<0 or if k>n. - Philippe Deléham, Nov 10 2013

EXAMPLE

Rows begin

1 1 2 4 8 ...

1 2 6 16 40 ...

1 3 12 40 120 ...

1 4 20 80 280 ...

1 5 30 140 560 ...

Read as a triangle, this begins:

1

1, 1

1, 2, 2

1, 3, 6, 4

1, 4, 12, 16, 8

1, 5, 20, 40, 40, 16

1, 6, 30, 80, 120, 96, 32

... - Philippe Deléham, Nov 10 2013

MAPLE

T := (n, k) -> binomial(n, k)*coeff(series((1-add(x^j, j=1..n))^(-1), x, k+2), x, k): seq(print(seq(T(n, k), k=0..n)), n=0..7); # Peter Luschny, Nov 03 2014

MATHEMATICA

rows = 11; t[n_, k_] := 2^(n-1)*(n+k)!/(n!*k!); t[0, _] = 1; tkn = Table[ t[n, k], {k, 0, rows}, {n, 0, rows}]; Flatten[ Table[ tkn[[ n-k+1, k ]], {n, 1, rows}, {k, 1, n}]] (* Jean-François Alcover, Jan 20 2012 *)

PROG

(Sage)

def A082137_row(n) : # as a triangular array

    var('z')

    s = (exp(z*x)/(1-tanh(x))).series(x, n+2)

    t = factorial(n)*s.coeff(x, n)

    return [t.coefficient(z, n-k) for k in (0..n)]

for n in (0..7) : print A082137_row(n)  # Peter Luschny, Aug 01 2012

CROSSREFS

Cf. A119468, A007318, A134309.

Sequence in context: A107230 A159830 A046726 * A091187 A065173 A098474

Adjacent sequences:  A082134 A082135 A082136 * A082138 A082139 A082140

KEYWORD

easy,nonn,tabl

AUTHOR

Paul Barry, Apr 06 2003

STATUS

approved

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

Content is available under The OEIS End-User License Agreement .

Last modified November 24 19:32 EST 2014. Contains 249909 sequences.