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Search: id:A116088
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| A116088 |
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Riordan array (1,x(1+x)^2). |
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+0
3
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| 1, 0, 1, 0, 2, 1, 0, 1, 4, 1, 0, 0, 6, 6, 1, 0, 0, 4, 15, 8, 1, 0, 0, 1, 20, 28, 10, 1, 0, 0, 0, 15, 56, 45, 12, 1, 0, 0, 0, 6, 70, 120, 66, 14, 1, 0, 0, 0, 1, 56, 210, 220, 91, 16, 1, 0, 0, 0, 0, 28, 252, 495, 364, 120, 18, 1
(list; table; graph; listen)
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OFFSET
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0,5
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COMMENT
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Row sums are A002478. Diagonal sums are A094686. Inverse is (-1)^(n-k)*A109971(n,k). Unsigned version of A109970.
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FORMULA
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G.f.: 1/(1-xy(1+x)^2); Number triangle T(n,k)=C(2k,n-k)=C(n,k)C(3k,n)/C(3k,k).
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EXAMPLE
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Triangle begins
1;
0, 1;
0, 2, 1;
0, 1, 4, 1;
0, 0, 6, 6, 1;
0, 0, 4,15, 8, 1;
0, 0, 1,20,28,10, 1;
0, 0, 0,15,56,45,12, 1;
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CROSSREFS
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Sequence in context: A118345 A118350 A109970 this_sequence A136501 A128307 A034369
Adjacent sequences: A116085 A116086 A116087 this_sequence A116089 A116090 A116091
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KEYWORD
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easy,nonn,tabl
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AUTHOR
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Paul Barry (pbarry(AT)wit.ie), Feb 04 2006
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