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 A129639 Number of meaningful differential operations of the k-th order on the space R^12. 4
 12, 22, 40, 74, 136, 252, 464, 860, 1584, 2936, 5408, 10024, 18464, 34224, 63040, 116848, 215232, 398944, 734848, 1362080, 2508928, 4650432, 8566016, 15877568, 29246208, 54209408, 99852800, 185082496, 340918784, 631911168, 1163969536 (list; graph; refs; listen; history; text; internal format)
 OFFSET 12,1 COMMENTS Also (starting 7,12,...) the number of zig-zag paths from top to bottom of a rectangle of width 7. [Joseph Myers, Dec 23 2008] LINKS 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. Branko Malesevic, Some combinatorial aspects of differential operation compositions on space R^n, arXiv:0704.0750 [math.DG], 2007. Joseph Myers, BMO 2008--2009 Round 1 Problem 1---Generalisation FORMULA f(k+6) = 6*f(k+4)-10*f(k+2)+4*f(k). Empirical G.f.: 2*x^12*(6+11*x-4*x^2-7*x^3)/(1-4*x^2+2*x^4). [Colin Barker, May 07 2012] MAPLE NUM := proc(k :: integer) local i, j, n, Fun, Identity, v, A; n:=12; # <- 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 f[k_] := f[k] = If[k <= 17, {12, 22, 40, 74, 136, 252}[[k-11]], 6 f[k-2] - 10 f[k-4] + 4 f[k-6]]; f /@ Range[12, 42] (* Jean-François Alcover, Apr 21 2020 *) CROSSREFS Cf. A090989, A090990, A090991, A090992, A090993, A090994, A090995. Sequence in context: A285470 A124885 A115745 * A153361 A200197 A115709 Adjacent sequences:  A129636 A129637 A129638 * A129640 A129641 A129642 KEYWORD nonn AUTHOR Branko Malesevic, May 31 2007 EXTENSIONS More terms from Joseph Myers, Dec 23 2008 STATUS approved

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Last modified October 6 15:48 EDT 2022. Contains 357269 sequences. (Running on oeis4.)