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 A090990 Number of meaningful differential operations of the n-th order on the space R^5. 6
 5, 9, 16, 29, 52, 94, 169, 305, 549, 990, 1783, 3214, 5790, 10435, 18801, 33881, 61048, 110009, 198224, 357194, 643633, 1159797, 2089869, 3765830, 6785771, 12227562, 22033274, 39702627, 71541613, 128913593, 232294192, 418579765 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also number of meaningful compositions of the n-th order of the differential operations and Gateaux directional derivative on the space R^4. - Branko Malesevic and Ivana Jovovic (ivana121(AT)EUnet.yu), Jun 21 2007 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 G. C. Greubel, Table of n, a(n) for n = 1..1000 B. Malesevic, Some combinatorial aspects of differential operation composition on the space R^n, arXiv:0704.0750 [math.DG], 2007. B. Malesevic and I. Jovovic, The Compositions of the Differential Operations and Gateaux Directional Derivative, arXiv:0706.0249 [math.CO], 2007. Index entries for linear recurrences with constant coefficients, signature (1,2,-1). FORMULA a(n+3) = a(n+2) + 2*a(n+1) - a(n). G.f.: x*(5+4*x-3*x^2)/(1-x-2*x^2+x^3). - Ralf Stephan, Aug 19 2004 MAPLE NUM := proc(k :: integer) local i, j, n, Fun, Identity, v, A; n := 5; # <- 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: MATHEMATICA LinearRecurrence[{1, 2, -1}, {5, 9, 16}, 32] (* Jean-François Alcover, Nov 22 2017 *) PROG (PARI) my(x='x+O('x^40)); Vec(x*(5+4*x-3*x^2)/(1-x-2*x^2+x^3)) \\ G. C. Greubel, Feb 02 2019 (MAGMA) m:=40; R:=PowerSeriesRing(Integers(), m); Coefficients(R!(  x*(5+4*x-3*x^2)/(1-x-2*x^2+x^3) )); // G. C. Greubel, Feb 02 2019 (Sage) a=(x*(5+4*x-3*x^2)/(1-x-2*x^2+x^3)).series(x, 40).coefficients(x, sparse=False); a[1:] # G. C. Greubel, Feb 02 2019 (GAP) a:=[5, 9, 16];; for n in [4..30] do a[n]:=a[n-1]+2*a[n-2]-a[n-3]; od; a; # G. C. Greubel, Feb 02 2019 CROSSREFS Cf. A090989, A090991, A090992, A090993, A090994, A090995. Cf. A000079, A007283, A020701, A020714, A129638. Sequence in context: A020958 A020750 A020713 * A225605 A088495 A218611 Adjacent sequences:  A090987 A090988 A090989 * A090991 A090992 A090993 KEYWORD nonn AUTHOR Branko Malesevic, Feb 29 2004 EXTENSIONS More terms from Ralf Stephan, Aug 19 2004 More terms from Branko Malesevic and Ivana Jovovic (ivana121(AT)EUnet.yu), Jun 21 2007 STATUS approved

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Last modified September 29 10:54 EDT 2020. Contains 337428 sequences. (Running on oeis4.)