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A072863
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a(n) = 2^(n-3)*(n^2+3*n+8).
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7
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1, 3, 9, 26, 72, 192, 496, 1248, 3072, 7424, 17664, 41472, 96256, 221184, 503808, 1138688, 2555904, 5701632, 12648448, 27918336, 61341696, 134217728, 292552704, 635437056, 1375731712, 2969567232, 6392119296, 13723762688
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OFFSET
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0,2
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COMMENTS
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Binomial transform of 1+n*(n+1)/2, A000124.
Number of 123-avoiding ternary words of length n-1.
Row sums of triangle A134247. Also double binomial transform of (1, 1, 1, 0, 0, 0, ...). - Gary W. Adamson, Oct 15 2007
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LINKS
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Tosic R., Masulovic D., Stojmenovic I., Brunvoll J., Cyvin B. N. and Cyvin S. J., Enumeration of polyhex hydrocarbons to h = 17, J. Chem. Inf. Comput. Sci., 1995, 35, 181-187, Table 1, with an error at h=16.
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FORMULA
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G.f.: (1-3x+3x^2)/(1-2x)^3;
a(n) = 2^(n-3)*(n^2+3n+8). (End)
E.g.f.: e^(2*x)*(1+x+x^2/2);
a(n) = Sum_{k=0..2} binomial(n,k)*2^(n-k). (End)
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MAPLE
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2^(n-3)*(n^2+3*n+8) ;
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MATHEMATICA
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Table[Sum[Binomial[m-1, k](#^2/2 -#/2 +1 &)[k+1], {k, 0, m}], {m, 36}]
LinearRecurrence[{6, -12, 8}, {1, 3, 9}, 30] (* Harvey P. Dale, May 15 2019 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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Michael A. Childers (childers_moof(AT)yahoo.com), Jul 27 2002
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EXTENSIONS
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New name using explicit formula. - Joerg Arndt, May 21 2018
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STATUS
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approved
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