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A216695
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Number of compositions (ordered partitions) of n into at least 2 distinct positive parts.
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3
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0, 0, 0, 2, 2, 4, 10, 12, 18, 26, 56, 64, 100, 132, 192, 350, 434, 616, 850, 1176, 1554, 2750, 3296, 4756, 6292, 8760, 11304, 15602, 24314, 30460, 41866, 55740, 74874, 98042, 130808, 168424, 257404, 315972, 431064, 558326, 751490, 958264, 1277866, 1621272, 2123586, 3020630, 3768440
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OFFSET
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0,4
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COMMENTS
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Inspired and generalized from Kakuro game, a Japanese crossword type game where cells must be filled with different digits 1..9 adding up to the clues.
If permutations are considered equivalent then a(n) = A111133(n) = A000009(n) - 1.
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LINKS
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FORMULA
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G.f.: (Sum_{k>=0} k!*x^((k^2+k)/2) / Product_{j=1..k} (1-x^j)) - 1/(1-x). - Joerg Arndt, Sep 17 2012
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EXAMPLE
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a(4)=2 because 4 = 1+3 = 3+1 (2 ways).
a(6)=10 because 6 = 1+5 = 2+4 = 4+2 = 5+1 = 1+2+3 = 1+3+2 = 2+1+3 = 2+3+1 = 3+1+2 = 3+2+1 (10 ways).
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MATHEMATICA
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nc[n_]:=Total[Length[#]!&/@Select[IntegerPartitions[n], Length[#]>1&&Max[ Tally[ #][[All, 2]]]==1&]]; Array[nc, 50, 0] (* Harvey P. Dale, May 27 2018 *)
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PROG
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(PARI)
N=66; x='x+O('x^N);
gf=sum(k=0, N, k!*x^((k^2+k)/2) / prod(j=1, k, 1-x^j)) - 1/(1-x);
v=Vec(gf);
vector(#v+1, n, if(n==1, 0, v[n-1]))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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