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 A026106 Number of polyhexes of class PF2 (with one catafusene annealated to pyrene). 9
 2, 5, 16, 55, 208, 817, 3336, 13935, 59406, 257079, 1126948, 4992421, 22318048, 100546543, 456055730, 2080872845, 9544572590, 43984730855, 203550840696, 945562887981, 4407586685688, 20609668887723, 96646196091276, 454402001079165 (list; graph; refs; listen; history; text; internal format)
 OFFSET 5,1 COMMENTS See reference for precise definition. From Petros Hadjicostas, Jan 12 2019: (Start) In Cyvin et al. (1992), sequence (N(m): m >= 1) = (A002212(m): m >= 1) is defined by eq. (1), p. 533. (We may let N(0) := A002212(0) = 1.) Sequence (M(m): m >= 1) is defined by eq. (13), p. 534. We have M(2*m) = M(2*m-1) =  A007317(m) for m >= 1. Sequences (N(m): m >= 1) and (M(m): m >= 1) appear in Table 1, p. 533. The current sequence is denoted by 1^Q_(4+n) (with n = 1,2,3,...). Thus, a(n+4) = 1^Q_(4+n) for n >= 1; i.e., a(m) = 1^Q_{m} for m >= 5. We have 1^Q_(4+n) = (1/2)*(3*N(n) + M(n)) for n >= 1. See eq. (33), p. 536. Sequence (1^Q_(4+n): n >= 1) appears in Table II, p. 537. We may use the many formulae in the documentations of sequences A002212 and A007317 in order to create complicated formulae and recurrence relations for (a(n): n >= 5). We omit the details. The first g.f. below is a combination of the g.f. for sequence A002212 by John W. Layman in 2001 and the g.f. for sequence A007317 by Ira M. Gessel and Jang Soo Kim in 2010. The second g.f. appears in eq. (A1), p. 1180, in Cyvin et al. (1994). It is algebraically equivalent to the first g.f. (Apparently, the word "annealated" in Cyvin et al. (1992) is spelled "annelated" in Cyvin et al. (1994).) (End) LINKS S. J. Cyvin, Zhang Fuji, B. N. Cyvin, Guo Xiaofeng, and J. Brunvoll, Enumeration and classification of benzenoid systems. 32. Normal perifusenes with two internal vertices, J. Chem. Inform. Comput. Sci., 32 (1992), 532-540. S. J. Cyvin, B. N. Cyvin, J. Brunvoll, and E. Brendsdal, Enumeration and classification of certain polygonal systems representing polycyclic conjugated hydrocarbons: annelated catafusenes, J. Chem. Inform. Comput. Sci., 34 (1994), 1174-1180. Eric Weisstein's World of Mathematics, Fusenes. Eric Weisstein's World of Mathematics, Polyhex. FORMULA From Petros Hadjicostas, Jan 12 2019: (Start) For n >= 1, a(n+4) = (1/2)*(3*A002212(n) + A007317(floor((n+1)/2))). G.f.: (x^3/4)*(4 - 8*x - 3*sqrt(1 - 6*x + 5*x^2) - (x + 1)*sqrt((1 - 5*x^2)/(1 - x^2))). G.f.: x^3*(1 - 2*x) - (x^3/4)*(3*(1 - x)^(1/2)*(1 - 5*x)^(1/2) + (1 - x)^(-1)*(1 - x^2)^(1/2)*(1 - 5*x^2)^(1/2)) (see eq. (A1), p. 1180, in Cyvin et al. (1994)). (End) MAPLE bb := proc(x) (1/4)*x^3*(4-8*x-3*sqrt((1-x)*(1-5*x))-(x+1)*sqrt((1-5*x^2)/(1-x^2))) end proc; taylor(bb(x), x = 0, 50); # Petros Hadjicostas, Jan 12 2019 CROSSREFS Cf. A002212, A007317, A026106, A026118, A026298, A030519, A030520, A030525, A030529, A030532, A030534, A039658. Sequence in context: A149971 A176828 A149972 * A308027 A066642 A019988 Adjacent sequences:  A026103 A026104 A026105 * A026107 A026108 A026109 KEYWORD nonn AUTHOR EXTENSIONS Name edited by Petros Hadjicostas, Jan 12 2019 Terms a(17)-a(28) computed by Petros Hadjicostas, Jan 12 2019 STATUS approved

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Last modified August 19 18:51 EDT 2019. Contains 326133 sequences. (Running on oeis4.)