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A155038
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Triangle read by rows: T(n,k) is the number of compositions of n with first part k.
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4
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1, 1, 1, 2, 1, 1, 4, 2, 1, 1, 8, 4, 2, 1, 1, 16, 8, 4, 2, 1, 1, 32, 16, 8, 4, 2, 1, 1, 64, 32, 16, 8, 4, 2, 1, 1, 128, 64, 32, 16, 8, 4, 2, 1, 1, 256, 128, 64, 32, 16, 8, 4, 2, 1, 1, 512, 256, 128, 64, 32, 16, 8, 4, 2, 1, 1, 1024, 512, 256, 128, 64, 32, 16, 8, 4, 2, 1, 1, 2048, 1024, 512
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OFFSET
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1,4
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COMMENTS
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Previous name was: Matrix inverse of A154990.
Apart from first term essentially the same as A057728.
Indexing the triangle from n=0 and k=0, T(n,k) is the number of binary words of length n that begin with a run of exactly k 0's. O.g.f.: 1/((1-y*x)*(1-x/(1-x))). - Geoffrey Critzer, Feb 15 2012
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LINKS
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FORMULA
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T(n,k) = 2^{n-k-1} if k<n; T(n,n) = 1; T(n,k) = 0 if k>n. - Emeric Deutsch, Jan 12 2018
G.f.: G(t,x) = (1-2x+tx^2)/(1-2x)(1-tx)). - Emeric Deutsch, Jan 19 2018
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EXAMPLE
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T(5,2) = 4 because the compositions of 5 with first part 2 are: [2,3], [2,2,1], [2,1,2], and [2,1,1,1]. - Emeric Deutsch, Jan 12 2018
Table begins:
1,
1, 1,
2, 1, 1,
4, 2, 1, 1,
8, 4, 2, 1, 1,
16, 8, 4, 2, 1, 1,
32, 16, 8, 4, 2, 1, 1,
64, 32, 16, 8, 4, 2, 1, 1,
Production matrix begins:
1, 1
1, 0, 1
1, 0, 0, 1
1, 0, 0, 0, 1
1, 0, 0, 0, 0, 1
1, 0, 0, 0, 0, 0, 1
1, 0, 0, 0, 0, 0, 0, 1
1, 0, 0, 0, 0, 0, 0, 0, 1
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MAPLE
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T := proc(n, k) if k = n then 1 elif k < n then 2^(n-k-1) else 0 end if end proc: for n to 13 do seq(T(n, k), k = 1 .. n) end do; # yields sequence in triangular form - Emeric Deutsch, Jan 12 2018
G:= (1-2*x+t*x^2)/((1-2*x)*(1-t*x)): Gser := simplify(series(G, x = 0, 15)): for n to 14 do P[n] := coeff(Gser, x, n) end do: for n to 14 do seq(coeff(P[n], t, j), j = 1 .. n) end do; # yields sequence in triangular form - Emeric Deutsch, Jan 19 2018
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MATHEMATICA
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nn = 15; a = 1/(1 - y x); f[list_] := Select[list, # > 0 &]; Map[f, CoefficientList[Series[ a/(1 - x/(1 - x)), {x, 0, nn}], {x, y}]] // Flatten (* Geoffrey Critzer, Feb 15 2012 *)
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PROG
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(Haskell)
a155038 n k = a155038_tabl !! (n-1) !! (k-1)
a155038_row n = a155038_tabl !! (n-1)
a155038_tabl = iterate
(\row -> zipWith (+) (row ++ [0]) (init row ++ [0, 1])) [1]
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CROSSREFS
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KEYWORD
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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