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A008999
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a(n) = 2 a(n-1) + a(n-4).
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8
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1, 2, 4, 8, 17, 36, 76, 160, 337, 710, 1496, 3152, 6641, 13992, 29480, 62112, 130865, 275722, 580924, 1223960, 2578785, 5433292, 11447508, 24118976, 50816737, 107066766, 225581040, 475281056, 1001378849
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 479
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FORMULA
| G.f.: 1/(1-2x-x^4) . - Philippe DELEHAM (kolotoko(AT)wanadoo.fr), Dec 02 2006
a(n)=sum(m=0..n, sum(j=0..(n-m)/3, binomial(n-m+(-3)*j,j)*binomial(n-3*j,m))). [From Vladimir Kruchinin (kru(AT)ie.tusur.ru), May 23 2011]
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MAPLE
| A008999 := proc(n) option remember; if n <= 3 then 2^n else 2*A008999(n-1)+A008999(n-4); fi; end;
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PROG
| (Maxima)
a(n):=sum(sum(binomial(n-m+(-3)*j, j)*binomial(n-3*j, m), j, 0, (n-m)/3), m, 0, n); [From Vladimir Kruchinin (kru(AT)ie.tusur.ru), May 23 2011]
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CROSSREFS
| Sequence in context: A098083 A182900 A202843 * A052903 A063457 A190162
Adjacent sequences: A008996 A008997 A008998 * A009000 A009001 A009002
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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