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A113125
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A simple tri-diagonal matrix.
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1
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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; internal format)
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OFFSET
| 0,3
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COMMENTS
| Row sums are A008486 (coordination sequence for graphite net). Diagonal sums are A026741(n+1). Diagonals are A000027.
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FORMULA
| Number triangle where column k has g.f. (1+x+x^2)(k+1)x^k.
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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;
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CROSSREFS
| Cf. A113126.
Sequence in context: A123590 A092872 A141455 * A088239 A130070 A082501
Adjacent sequences: A113122 A113123 A113124 * A113126 A113127 A113128
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KEYWORD
| easy,nonn,tabl
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AUTHOR
| Paul Barry (pbarry(AT)wit.ie), Oct 14 2005
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