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A224959
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Number of compositions [p(1), p(2), ..., p(k)] of n such that p(j) - p(j-1) <= 2
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4
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1, 1, 2, 4, 8, 15, 29, 55, 105, 199, 378, 716, 1358, 2572, 4873, 9229, 17480, 33102, 62688, 118709, 224795, 425676, 806068, 1526371, 2890338, 5473125, 10363871, 19624925, 37161558, 70368705, 133249369, 252319408, 477788980, 904735349, 1713195705, 3244086145
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OFFSET
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0,3
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LINKS
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FORMULA
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a(n) ~ c * d^n, where d=1.893587506319686491635881459546948770530553555112342985931092896452453511... and c=0.6398882559654423774981963082429746674258714212085034829366885993226... - Vaclav Kotesovec, May 01 2014
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EXAMPLE
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There are a(5) = 15 such compositions of 5:
01: [ 1 1 1 1 1 ]
02: [ 1 1 1 2 ]
03: [ 1 1 2 1 ]
04: [ 1 1 3 ]
05: [ 1 2 1 1 ]
06: [ 1 2 2 ]
07: [ 1 3 1 ]
08: [ 2 1 1 1 ]
09: [ 2 1 2 ]
10: [ 2 2 1 ]
11: [ 2 3 ]
12: [ 3 1 1 ]
13: [ 3 2 ]
14: [ 4 1 ]
15: [ 5 ]
(the single forbidden composition is [ 1 4 ]).
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MAPLE
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b:= proc(n, i) option remember;
`if`(n=0, 1, add(b(n-j, max(1, j-2)), j=i..n))
end:
a:= n-> b(n, 1):
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MATHEMATICA
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b[n_, i_] := b[n, i] = If[n==0, 1, Sum[b[n-j, Max[1, j-2]], {j, i, n}]];
a[n_] := b[n, 1];
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CROSSREFS
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Cf. A003116 (compositions such that p(j) - p(j-1) <= 1).
Cf. A225084 (triangle: compositions of n such that max(p(j) - p(j-1)) = k).
Cf. A225085 (triangle: compositions of n such that max(p(j) - p(j-1)) <= k).
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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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