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A090989
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Number of meaningful differential operations of the n-th order on the space R^4.
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14
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4, 6, 8, 12, 16, 24, 32, 48, 64, 96, 128, 192, 256, 384, 512, 768, 1024, 1536, 2048, 3072, 4096, 6144, 8192, 12288, 16384, 24576, 32768, 49152, 65536, 98304, 131072, 196608, 262144, 393216, 524288, 786432, 1048576, 1572864, 2097152, 3145728, 4194304, 6291456, 8388608
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OFFSET
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1,1
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LINKS
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FORMULA
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a(k+2) = 2*a(k).
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MAPLE
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NUM := proc(k :: integer) local i, j, n, Fun, Identity, v, A; n := 4; # <- DIMENSION Fun := (i, j)->piecewise(((j=i+1) or (i+j=n+1)), 1, 0); Identity := (i, j)->piecewise(i=j, 1, 0); v := matrix(1, n, 1); A := piecewise(k>1, (matrix(n, n, Fun))^(k-1), k=1, matrix(n, n, Identity)); return(evalm(v&*A&*transpose(v))[1, 1]); end:
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MATHEMATICA
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LinearRecurrence[{0, 2}, {4, 6}, 40] (* G. C. Greubel, Feb 02 2019 *)
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PROG
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(PARI) my(x='x+O('x^40)); Vec(2*x*(2+3*x)/(1-2*x^2)) \\ G. C. Greubel, Feb 02 2019
(Magma) m:=40; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!( 2*x*(2+3*x)/(1-2*x^2) )); // G. C. Greubel, Feb 02 2019
(Sage) (2*(2+3*x)/(1-2*x^2)).series(x, 40).coefficients(x, sparse=False) # G. C. Greubel, Feb 02 2019
(GAP) a:=[4, 6];; for n in [3..40] do a[n]:=2*a[n-2]; od; a; # G. C. Greubel, Feb 02 2019
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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