

A055373


Invert transform applied twice to Pascal's triangle A007318.


2



1, 1, 1, 3, 6, 3, 9, 27, 27, 9, 27, 108, 162, 108, 27, 81, 405, 810, 810, 405, 81, 243, 1458, 3645, 4860, 3645, 1458, 243, 729, 5103, 15309, 25515, 25515, 15309, 5103, 729, 2187, 17496, 61236, 122472, 153090, 122472, 61236, 17496, 2187, 6561
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OFFSET

0,4


COMMENTS

Triangle T(n,k), 0 <= k <= n, read by rows, given by [1, 2, 0, 0, 0, 0, 0, 0, 0, ...] DELTA [1, 2, 0, 0, 0, 0, 0, 0, 0, ...] where DELTA is the operator defined in A084938.  Philippe Deléham, Aug 10 2005
T(n,k) is the number of sequences of nonempty sequences of nonempty bit strings with n bits and exactly k 1's over all strings in the sequence of sequences. In other words these are sequences of the structures counted by A055372.  Geoffrey Critzer, Apr 06 2013


LINKS

Table of n, a(n) for n=0..45.
N. J. A. Sloane, Transforms
Index entries for triangles and arrays related to Pascal's triangle


FORMULA

T(n,k) = 3^(n1)*C(n, k) for n>0.
O.g.f.: 1/(2  A(x,y)) where A(x,y) is the o.g.f. for A055372.  Geoffrey Critzer, Apr 06 2013


EXAMPLE

Triangle begins:
1;
1,1;
3,6,3;
9,27,27,9;
27,108,162,108,27;
...


MATHEMATICA

nn=10; f[list_]:=Select[list, #>0&]; a=(x+y x)/(1(x+y x)); b=1/(1a); Map[f, CoefficientList[Series[1/(2b), {x, 0, nn}], {x, y}]]//Grid (* Geoffrey Critzer, Apr 06 2013 *)


CROSSREFS

Cf. A000244, A007318, A055372, A055374.
Sequence in context: A065231 A019918 A260303 * A263333 A328371 A134440
Adjacent sequences: A055370 A055371 A055372 * A055374 A055375 A055376


KEYWORD

nonn,tabl


AUTHOR

Christian G. Bower, May 16 2000


STATUS

approved



