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 A006414 Number of nonseparable toroidal tree-rooted maps on n nodes. (Formerly M4621) 11
 1, 9, 40, 125, 315, 686, 1344, 2430, 4125, 6655, 10296, 15379, 22295, 31500, 43520, 58956, 78489, 102885, 133000, 169785, 214291, 267674, 331200, 406250, 494325, 597051, 716184, 853615, 1011375, 1191640, 1396736, 1629144, 1891505, 2186625, 2517480, 2887221 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS a(n) = K(Oa(2,3,n)), Kekulé numbers of certain benzenoid structures (see the Cyvin - Gutman reference). Sequence of partial sums of A006322. - L. Edson Jeffery, Dec 13 2011 The sequence b(n) = a(n-2) with a(-1) = 0, for n >= 1, is b(n) = n^3*(n^2 - 1)/4!. It is obtained by comparing the result for the powers n^5 from Worpitzky's identity (see a formula in A000584) with the result obtained from the counting of degrees of freedom for the decomposition of a rank 5 tensor in n dimensions via the standard Young tableaux version with 5 boxes corresponding to the seven partitions of 5. The difference of the two versions gives: 10*(binomial(n+3, 5) + 3*binomial(n+2, 5) + binomial(n+1, 5)) = 5*n*(binomial(n+2, 4) + binomial(n+1, 4)) = 10*b(n). See the formula for a(n) below. - Wolfdieter Lang, Jul 18 2019 REFERENCES S. J. Cyvin and I. Gutman, Kekulé structures in benzenoid hydrocarbons, Lecture Notes in Chemistry, No. 46, Springer, New York, 1988, p. 105, eq. (ii). 187). 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..10000 T. R. S. Walsh, A. B. Lehman, Counting rooted maps by genus. III: Nonseparable maps, J. Combinatorial Theory Ser. B 18 (1975), 222-259. Index entries for linear recurrences with constant coefficients, signature (6,-15,20,-15,6,-1). FORMULA a(n) = (n+1)*(n+2)^3*(n+3)/24. - N. J. A. Sloane, Apr 02 2004 a(n) = (n+2)^3*((n+2)^2 - 1)/24. - Paul Richards, Mar 04 2007 G.f.: (1 + 3*x + x^2)/(1-x)^6. - Colin Barker, Feb 21 2012 a(n) = (Sum_{k=0..n+1} k*(n+1)*((n+1)^2 - k^2))/6 for n > 0, which is the sum of all areas of Pythagorean triangles with arms 2*k*(n+1) and (n+1)^2 - k^2 with hypotenuse k^2 + (n+1)^2. - J. M. Bergot, May 12 2014 a(n) = A143945(n+2)/8. - J. M. Bergot, Jun 14 2014 Sum_{n>=0} 1/a(n) = 30 - 24*zeta(3). - Jaume Oliver Lafont, Jul 09 2017 a(n) = binomial(n+5, 5) + 3*binomial(n+4, 5) + binomial(n+3, 5) = ((n+2)/2)*(binomial(n+4, 4) + binomial(n+3, 4)), for n >= 0. See a comment above on the sequence b(n) = a(n-2) = n^3*(n^2 - 1)/4!. - Wolfdieter Lang, Jul 19 2019 E.g.f.: (24 + 192*x + 276*x^2 + 124*x^3 + 20*x^4 + x^5)*exp(x)/4!. - G. C. Greubel, Sep 02 2019 MAPLE seq((n+2)^2*binomial(n+3, 3)/4, n=0..40); # G. C. Greubel, Sep 02 2019 MATHEMATICA Table[(n + 1)*(n + 2)^3*(n + 3)/24, {n, 0, 40}] (* Vladimir Joseph Stephan Orlovsky, Apr 18 2011 *) PROG (MAGMA) [(n+1)*(n+2)^3*(n+3)/24: n in [0..40]]; // Wesley Ivan Hurt, May 10 2014 (PARI) a(n) = (n+1)*(n+2)^3*(n+3)/24; \\ Michel Marcus, Jul 09 2017 (Sage) [(n+2)^2*binomial(n+3, 3)/4 for n in (0..40)] # G. C. Greubel, Sep 02 2019 (GAP) List([0..40], n-> (n+2)^2*Binomial(n+3, 3)/4 ); G. C. Greubel, Sep 02 2019 CROSSREFS Differences of A006542 (C(n, 3)*C(n-1, 3)/4). Cf. A004068, A005891, A006322, A133754, A143945. Sequence in context: A165372 A264624 A287324 * A213758 A181960 A219511 Adjacent sequences:  A006411 A006412 A006413 * A006415 A006416 A006417 KEYWORD nonn,easy AUTHOR EXTENSIONS More terms from Robert Newstedt (Patternfinder(AT)webtv.net) STATUS approved

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Last modified February 19 18:44 EST 2020. Contains 332047 sequences. (Running on oeis4.)