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A131909 Triangle, read by rows, where T(n,k) = T(n-1,k-2) + T(n-1,k-1) for n>=k>1, with T(0,0)=1 and T(n,0) = T(n+1,1) = T(n-1,n-1) for n>0. 1
1, 1, 1, 1, 1, 2, 2, 1, 2, 3, 3, 2, 3, 3, 5, 5, 3, 5, 5, 6, 8, 8, 5, 8, 8, 10, 11, 14, 14, 8, 13, 13, 16, 18, 21, 25, 25, 14, 22, 21, 26, 29, 34, 39, 46, 46, 25, 39, 36, 43, 47, 55, 63, 73, 85, 85, 46, 71, 64, 75, 79, 90, 102, 118, 136, 158, 158, 85, 131, 117, 135, 139, 154, 169 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

0,6

COMMENTS

A119262(n) is the number of B-trees of order infinity with n leaves.

LINKS

Table of n, a(n) for n=0..73.

FORMULA

Row sums equal powers of 2. T(n,0) = A119262(n+1) for n>=0, where g.f. G(x) of A119262 satisfies: G(x) = x + G(x^2/(1-x)).

EXAMPLE

Triangle begins:

1;

1, 1;

1, 1, 2;

2, 1, 2, 3;

3, 2, 3, 3, 5;

5, 3, 5, 5, 6, 8;

8, 5, 8, 8, 10, 11, 14;

14, 8, 13, 13, 16, 18, 21, 25;

25, 14, 22, 21, 26, 29, 34, 39, 46;

46, 25, 39, 36, 43, 47, 55, 63, 73, 85;

85, 46, 71, 64, 75, 79, 90, 102, 118, 136, 158;

158, 85, 131, 117, 135, 139, 154, 169, 192, 220, 254, 294; ...

Illustrate T(n,k) = T(n-1,k-2) + T(n-1,k-1):

T(5,3) = T(4,1) + T(4,2) = 2 + 3 = 5;

T(6,4) = T(5,2) + T(5,3) = 5 + 5 = 10;

T(8,3) = T(7,1) + T(7,2) = 8 +13 = 21.

PROG

(PARI) T(n, k)=if(k<0 || n<k, 0, if(n==0 && k==0, 1, if(k==0, T(n-1, n-1), T(n-1, k-2)+T(n-1, k-1))))

CROSSREFS

Cf. A119262 (columns 0, 1 and main diagonal); A131910 (central terms).

Sequence in context: A256478 A106638 A329400 * A307319 A131730 A029335

Adjacent sequences:  A131906 A131907 A131908 * A131910 A131911 A131912

KEYWORD

nonn,tabl

AUTHOR

Paul D. Hanna, Jul 26 2007

STATUS

approved

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Last modified May 17 03:43 EDT 2022. Contains 353727 sequences. (Running on oeis4.)