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 A006522 4-dimensional analog of centered polygonal numbers. Also number of regions created by sides and diagonals of n-gon in general position. (Formerly M3413) 17
 1, 0, 0, 1, 4, 11, 25, 50, 91, 154, 246, 375, 550, 781, 1079, 1456, 1925, 2500, 3196, 4029, 5016, 6175, 7525, 9086, 10879, 12926, 15250, 17875, 20826, 24129, 27811, 31900, 36425, 41416, 46904, 52921, 59500, 66675, 74481, 82954, 92131 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 COMMENTS Let A be the Hessenberg matrix of order n, defined by: A[1,j]=A[i,i]:=1, A[i,i-1]=-1, and A[i,j]=0 otherwise. Then, for n>=5, a(n)=coeff(charpoly(A,x),x^(n-4)). - Milan Janjic, Jan 24 2010 From Ant King, Sep 14 2011: (Start) Consider the array formed by the polygonal numbers of increasing rank A139600 0, 1, 3,  6, 10, 15, 21,  28,  36,  45, ...  A000217(n) 0, 1, 4,  9, 16, 25, 36,  49,  64,  81, ...  A000290(n) 0, 1, 5, 12, 22, 35, 51,  70,  92, 117, ...  A000326(n) 0, 1, 6, 15, 28, 45, 66,  91, 120, 153, ...  A000384(n) 0, 1, 7, 18, 34, 55, 81, 112, 148, 189, ...  A000566(n) 0, 1, 8, 21, 40, 65, 96, 133, 176, 225, ...  A000567(n) ... Then, for n>=2, a(n) is the diagonal sum of this polygonal grid. (End) Binomial transform of (1, -1, 1, 0, 1, 0, 0, 0, ...). - Gary W. Adamson, Aug 26 2015 REFERENCES L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 74, Problem 8. R. Honsberger, Mathematical Gems, M.A.A., 1973, p. 102. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 J. W. Freeman, The number of regions determined by a convex polygon, Math. Mag., 49 (1976), 23-25. Math Forum, Regions of a circle Cut by Chords to n points. V. Meally, Letter to N. J. A. Sloane, May 1975 M. Janjic, Hessenberg Matrices and Integer Sequences , J. Int. Seq. 13 (2010) # 10.7.8 Simon Plouffe, Approximations de séries génératrices et quelques conjectures, Dissertation, Université du Québec à Montréal, 1992. Simon Plouffe, 1031 Generating Functions and Conjectures, Université du Québec à Montréal, 1992. Eric Weisstein's World of Mathematics, Polygon Diagonal. Index entries for linear recurrences with constant coefficients, signature (5, -10, 10, -5, 1). FORMULA a(n) = binomial(n, 4)+ binomial(n-1, 2). a(n) = binomial(n,2) + binomial(n,3) + binomial(n,4), n>=-1. - Zerinvary Lajos, Jul 23 2006 a(0)=1, a(1)=0, a(2)=0, a(3)=1, a(4)=4, a(n) = 5*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5). - Harvey P. Dale, Jul 11 2011 G.f.: -((x-1)*x*(x*(4*x-5)+5)+1)/(x-1)^5. - Harvey P. Dale, Jul 11 2011 a(n) = (n^4 - 6*n^3 + 23*n^2 - 42*n + 24)/24. - T. D. Noe, Oct 16 2013 For odd n, a(n) = A007678(n). - R. J. Mathar, Nov 22 2017 EXAMPLE For a pentagon in general position, 11 regions are formed (Comtet, Fig. 20, p. 74). MAPLE A006522 := n->(1/24)*(n-1)*(n-2)*(n^2-3*n+12); [seq(binomial(n, 2)+binomial(n, 3)+binomial(n, 4), n=-1..40)]; # Zerinvary Lajos, Jul 23 2006 A006522:=-(1-z+z**2)/(z-1)**5; # Simon Plouffe in his 1992 dissertation; gives sequence except for three leading terms MATHEMATICA a=2; b=3; s=4; lst={1, 0, 0, 1, s}; Do[a+=n; b+=a; s+=b; AppendTo[lst, s], {n, 2, 6!, 1}]; lst (* Vladimir Joseph Stephan Orlovsky, May 24 2009 *) Table[Binomial[n, 4]+Binomial[n-1, 2], {n, 0, 40}] (* or *) LinearRecurrence[ {5, -10, 10, -5, 1}, {1, 0, 0, 1, 4}, 40] (* Harvey P. Dale, Jul 11 2011 *) CoefficientList[Series[-(((x - 1) x (x (4 x - 5) + 5) + 1) / (x - 1)^5), {x, 0, 50}], x] (* Vincenzo Librandi, Jun 09 2013 *) PROG (MAGMA) [Binomial(n, 4)+Binomial(n-1, 2): n in [0..40]]; // Vincenzo Librandi, Jun 09 2013 (PARI) a(n)=1/24*n^4 - 1/4*n^3 + 23/24*n^2 - 7/4*n + 1 \\ Charles R Greathouse IV, Feb 09 2017 CROSSREFS Partial sums of A004006. Sequence in context: A051462 A006004 A290876 * A036837 A215052 A011851 Adjacent sequences:  A006519 A006520 A006521 * A006523 A006524 A006525 KEYWORD nonn,easy,nice AUTHOR STATUS approved

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Last modified December 13 22:42 EST 2018. Contains 318087 sequences. (Running on oeis4.)