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A369806
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Expansion of 1/(1 - x^3/(1-x)^7).
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4
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1, 0, 0, 1, 7, 28, 85, 224, 567, 1485, 4117, 11802, 33909, 96182, 269402, 750275, 2090728, 5845015, 16384908, 45973701, 128944042, 361364501, 1012168575, 2834690172, 7939970075, 22244001961, 62323608147, 174620915138, 489240430938, 1370662332271, 3839992876850
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OFFSET
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0,5
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COMMENTS
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Number of compositions of 7*n-3 into parts 3 and 7.
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LINKS
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FORMULA
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a(n) = 7*a(n-1) - 21*a(n-2) + 36*a(n-3) - 35*a(n-4) + 21*a(n-5) - 7*a(n-6) + a(n-7) for n > 7.
a(n) = Sum_{k=0..floor(n/3)} binomial(n-1+4*k,n-3*k).
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PROG
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(PARI) my(N=40, x='x+O('x^N)); Vec(1/(1-x^3/(1-x)^7))
(PARI) a(n) = sum(k=0, n\3, binomial(n-1+4*k, n-3*k));
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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