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Search: id:A117375
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| A117375 |
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Riordan array (1/(1-3x*c(x)),xc(x)), c(x) the g.f. of A000108. |
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+0
3
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| 1, 3, 1, 12, 4, 1, 51, 17, 5, 1, 222, 74, 23, 6, 1, 978, 326, 104, 30, 7, 1, 4338, 1446, 468, 142, 38, 8, 1, 19323, 6441, 2103, 657, 189, 47, 9, 1, 86310, 28770, 9447, 3006, 903, 246, 57, 10, 1, 386250, 128750, 42440, 13670, 4223, 1217, 314, 68, 11, 1, 1730832
(list; table; graph; listen)
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OFFSET
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0,2
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COMMENT
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Triangle factorises as (1,xc(x))*(1/(1-3x),x). First row is A007854. Second row is A049027(n)-0^n. Row sums are A049027(n+1). Diagonal sums are A117376.
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FORMULA
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Number triangle T(0,0)=1, T(n,k)=[k<=n]*sum{j=0..n, (j/(n-j))*C(2n-j,n-j)[k<=j]*3^(j-k)}
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EXAMPLE
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Triangle begins
1,
3, 1,
12, 4, 1,
51, 17, 5, 1,
222, 74, 23, 6, 1,
978, 326, 104, 30, 7, 1,
4338, 1446, 468, 142, 38, 8, 1
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CROSSREFS
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Sequence in context: A144880 A144881 A121420 this_sequence A122844 A113369 A127894
Adjacent sequences: A117372 A117373 A117374 this_sequence A117376 A117377 A117378
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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), Mar 10 2006
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