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A038221
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Triangle whose (i,j)-th entry is binomial(i,j)*3^(i-j)*3^j.
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3
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1, 3, 3, 9, 18, 9, 27, 81, 81, 27, 81, 324, 486, 324, 81, 243, 1215, 2430, 2430, 1215, 243, 729, 4374, 10935, 14580, 10935, 4374, 729, 2187, 15309, 45927, 76545, 76545, 45927, 15309, 2187, 6561, 52488, 183708, 367416, 459270, 367416
(list;
table;
graph;
refs;
listen;
history;
text;
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OFFSET
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0,2
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REFERENCES
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B. N. Cyvin et al., Isomer enumeration of unbranched catacondensed polygonal systems with pentagons and heptagons, Match, No. 34 (Oct 1996), pp. 109-121.
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LINKS
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Table of n, a(n) for n=0..41.
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PROG
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(Haskell)
a038221 n = a038221_list !! n
a038221_list = concat $ iterate ([3, 3] *) [1]
instance Num a => Num [a] where
fromInteger k = [fromInteger k]
(p:ps) + (q:qs) = p + q : ps + qs
ps + qs = ps ++ qs
(p:ps) * qs'@(q:qs) = p * q : ps * qs' + [p] * qs
_ * _ = []
-- Reinhard Zumkeller, Apr 02 2011
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CROSSREFS
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Sequence in context: A100744 A217450 A089892 * A099465 A099094 A222169
Adjacent sequences: A038218 A038219 A038220 * A038222 A038223 A038224
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KEYWORD
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nonn,tabl,easy
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AUTHOR
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N. J. A. Sloane.
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STATUS
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approved
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