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A113125 A simple tri-diagonal matrix. 1
1, 1, 2, 1, 2, 3, 0, 2, 3, 4, 0, 0, 3, 4, 5, 0, 0, 0, 4, 5, 6, 0, 0, 0, 0, 5, 6, 7, 0, 0, 0, 0, 0, 6, 7, 8, 0, 0, 0, 0, 0, 0, 7, 8, 9, 0, 0, 0, 0, 0, 0, 0, 8, 9, 10, 0, 0, 0, 0, 0, 0, 0, 0, 9, 10, 11, 0, 0, 0, 0, 0, 0, 0, 0, 0, 10, 11, 12, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 11, 12, 13, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Row sums are A008486 (coordination sequence for graphite net). Diagonal sums are A026741(n+1). Diagonals are A000027.

LINKS

Table of n, a(n) for n=0..100.

FORMULA

Number triangle where column k has g.f. (1+x+x^2)(k+1)x^k.

EXAMPLE

Triangle begins

1;

1,2;

1,2,3;

0,2,3,4;

0,0,3,4,5;

0,0,0,4,5,6;

0,0,0,0,5,6,7;

0,0,0,0,0,6,7,8;

CROSSREFS

Cf. A113126.

Sequence in context: A092872 A141455 A292627 * A088239 A130070 A273516

Adjacent sequences:  A113122 A113123 A113124 * A113126 A113127 A113128

KEYWORD

easy,nonn,tabl

AUTHOR

Paul Barry, Oct 14 2005

STATUS

approved

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Last modified August 11 09:47 EDT 2020. Contains 336423 sequences. (Running on oeis4.)