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 A003116 Expansion of the reciprocal of the g.f. defining A039924. (Formerly M1068) 23
 1, 1, 2, 4, 7, 13, 23, 41, 72, 127, 222, 388, 677, 1179, 2052, 3569, 6203, 10778, 18722, 32513, 56455, 98017, 170161, 295389, 512755, 890043, 1544907, 2681554, 4654417, 8078679, 14022089, 24337897, 42242732, 73319574, 127258596, 220878683 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Conjecture: a(n) is the number of compositions p(1) + p(2) + ... + p(m) = n with p(i)-p(i-1) <= 1, see example; cf. A034297. - Vladeta Jovovic, Feb 09 2004 Row sums and central terms of the triangle in A168396: a(n) = A168396(2*n+1,n) and for n > 0: a(n) = Sum_{k=1..n} A168396(n,k). - Reinhard Zumkeller, Sep 13 2013 Former definition was "Expansion of reciprocal of a determinant." - N. J. A. Sloane, Aug 10 2018 From Doron Zeilberger, Aug 10 2018: (Start) Jovovic's conjecture can be proved as follows. There is a sign-changing involution defined on pairs (L1,L2) where L1 is a partition with difference >= 2 between consecutive parts and L2 is the number of compositions described by Jovovic, with the sign (-1)^(Number of parts of L1). Let a be the largest part of L1 and b the largest part of L2. If b-a>=2 then move b from L2 to the top of L1, otherwise move a to the top of L2. Since this is an involution and it changes the sign (the number of parts of L1 changes parity) this proves it, since the g.f. of A039924 is exactly the signed-enumeration of the set given by L1. (End) REFERENCES Lehmer, D. H. Combinatorial and cyclotomic properties of certain tridiagonal matrices. Proceedings of the Fifth Southeastern Conference on Combinatorics, Graph Theory, and Computing (Florida Atlantic Univ., Boca Raton, Fla., 1974), pp. 53-74. Congressus Numerantium, No. X, Utilitas Math., Winnipeg, Man., 1974. MR0441852. H. P. Robinson, Letter to N. J. A. Sloane, Nov 19 1973. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Alois P. Heinz, Table of n, a(n) for n = 0..4176 (first 401 terms from T. D. Noe) Shalosh B. Ekhad, Doron Zeilberger, D.H. Lehmer's Tridiagonal determinant: An Etude in (Andrews-Inspired) Experimental Mathematics, arXiv:1808.06730 [math.CO], 2018. Herman P. Robinson, Letter to N. J. A. Sloane, Nov 13 1973. Herman P. Robinson, Letter to N. J. A. Sloane, Nov 19 1973. FORMULA G.f.: 1/(Sum_{k>=0} x^(k^2)(-1)^k/(Product_{i=1..k} 1-x^i)). EXAMPLE From Joerg Arndt, Dec 29 2012: (Start) There are a(6)=23 compositions p(1)+p(2)+...+p(m)=6 such that p(k)-p(k-1) <= 1: [ 1]  [ 1 1 1 1 1 1 ] [ 2]  [ 1 1 1 1 2 ] [ 3]  [ 1 1 1 2 1 ] [ 4]  [ 1 1 2 1 1 ] [ 5]  [ 1 1 2 2 ] [ 6]  [ 1 2 1 1 1 ] [ 7]  [ 1 2 1 2 ] [ 8]  [ 1 2 2 1 ] [ 9]  [ 1 2 3 ] [10]  [ 2 1 1 1 1 ] [11]  [ 2 1 1 2 ] [12]  [ 2 1 2 1 ] [13]  [ 2 2 1 1 ] [14]  [ 2 2 2 ] [15]  [ 2 3 1 ] [16]  [ 3 1 1 1 ] [17]  [ 3 1 2 ] [18]  [ 3 2 1 ] [19]  [ 3 3 ] [20]  [ 4 1 1 ] [21]  [ 4 2 ] [22]  [ 5 1 ] [23]  [ 6 ] Replacing the condition with p(k)-p(k-1) <= 0 gives integer partitions. (End) MATHEMATICA max = 35; f[x_] := 1/Sum[x^k^2*((-1)^k/Product[1 - x^i, {i, 1, k}]), {k, 0, Floor[Sqrt[max]]}]; CoefficientList[ Series[f[x], {x, 0, max}], x](* Jean-François Alcover, Jun 12 2012, after PARI *) PROG (PARI) a(n)=if(n<0, 0, polcoeff(1/sum(k=0, sqrtint(n), x^k^2/prod(i=1, k, x^i-1, 1+x*O(x^n))), n)) (Haskell) a003116 n = a168396 (2 * n + 1) n  -- Reinhard Zumkeller, Sep 13 2013 CROSSREFS Cf. A003114, A039924, A034297, A224959. Sequence in context: A319255 A136299 A208354 * A303666 A260917 A165648 Adjacent sequences:  A003113 A003114 A003115 * A003117 A003118 A003119 KEYWORD nonn,nice,easy AUTHOR EXTENSIONS Definition revised by N. J. A. Sloane, Aug 10 2018 at the suggestion of Doron Zeilberger STATUS approved

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Last modified October 15 03:30 EDT 2019. Contains 328025 sequences. (Running on oeis4.)