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 A090989 Number of meaningful differential operations of the n-th order on the space R^4. 13
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES B. Malesevic: Some combinatorial aspects of differential operation composition on the space R^n, Univ. Beograd, Publ. Elektrotehn. Fak., Ser. Mat. 9 (1998), 29-33. LINKS Index entries for linear recurrences with constant coefficients, signature (0,2). FORMULA a(k+2)=2*a(k). a(n)= gcdConv(0, {A000079})[n+3]. -  Tilman Neumann, Jan 11 2009 G.f.: 2*x*(2+3*x)/(1-2*x^2). [Colin Barker, May 03 2012] MAPLE 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: CROSSREFS Cf. A063759, A029744, A090990-A090995. Sequence in context: A020225 A162294 A211026 * A161219 A161785 A234523 Adjacent sequences:  A090986 A090987 A090988 * A090990 A090991 A090992 KEYWORD nonn,easy AUTHOR Branko Malesevic, Feb 29 2004 EXTENSIONS More terms from Tilman Neumann, Feb 06 2009 STATUS approved

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