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 A018210 Alkane (or paraffin) numbers l(9,n). 4
 1, 4, 16, 44, 110, 236, 472, 868, 1519, 2520, 4032, 6216, 9324, 13608, 19440, 27192, 37389, 50556, 67408, 88660, 115258, 148148, 188552, 237692, 297115, 368368, 453376, 554064, 672792, 811920, 974304, 1162800, 1380825, 1631796 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS From M. F. Hasler, May 02 2009: (Start) Also, 6th column of A159916, i.e., number of 6-element subsets of {1,...,n+6} whose elements add up to an odd integer. Third differences are A002412([n/2]). (End) F(1,6,n) is the number of bracelets with 1 blue, 6 identical red and n identical black beads. If F(1,6,1) = 4 and F(1,6,2) = 16 taken as a base, F(1,6,n) = n(n+1)(n+2)(n+3)(n+4)/120 + F(1,4,n) + F(1,6,n-2). F(1,4,n) is the number of bracelets with 1 blue, 4 identical red and n identical black beads. If F(1,4,1) = 3 and F(1,4,2) = 9 taken as a base; F(1,4,n) = n(n+1)(n+2)/6 + F(1,2,n) + F(1,4,n-2). F(1,2,n) is the number of bracelets with 1 blue, 2 identical red and n identical black beads. If F(1,2,1) = 2 and F(1,2,2) = 4 taken as a base F(1,2,n) = n + 1 + F(1,2,n-2). - Ata Aydin Uslu and Hamdi G. Ozmenekse, Mar 16 2012 REFERENCES S. M. Losanitsch, Die Isomerie-Arten bei den Homologen der Paraffin-Reihe, Chem. Ber. 30 (1897), 1917-1926. Winston C. Yang (paper in preparation). LINKS N. J. A. Sloane, Classic Sequences Ata A. Uslu and Hamdi G. Ozmenekse, F(1,6,n) Ata A. Uslu and Hamdi G. Ozmenekse, F(1,4,n) Ata A. Uslu and Hamdi G. Ozmenekse, F(1,2,n) Index entries for linear recurrences with constant coefficients, signature (4, -3, -8, 14, 0, -14, 8, 3, -4, 1). FORMULA G.f.: (1+3*x^2)/(1-x)^4/(1-x^2)^3. - N. J. A. Sloane l(c, r) = 1/2 C(c+r-3, r) + 1/2 d(c, r), where d(c, r) is C((c + r - 3)/2, r/2) if c is odd and r is even, 0 if c is even and r is odd, C((c + r - 4)/2, r/2) if c is even and r is even, C((c + r - 4)/2, (r - 1)/2) if c is odd and r is odd. a(2n) = (n+1)(n+2)(n+3)^2(4n^2+6n+5)/90, a(2n-1) = n(n+1)(n+2)(n+3)(4n^2+6n+5)/90. - M. F. Hasler, May 02 2009 a(n) = (1/(2*6!))*(n+2)*(n+4)*(n+6)*((n+1)*(n+3)*(n+5) + 1*3*5) - (1/2)*(1/2^4)*(n^2+7*n+11)*(1/2)*(1-(-1)^n). - Yosu Yurramendi, Jun 23 2013 MAPLE a:=n-> (Matrix([[1, 0\$7, 3, 12]]). Matrix(10, (i, j)-> if (i=j-1) then 1 elif j=1 then [4, -3, -8, 14, 0, -14, 8, 3, -4, 1][i] else 0 fi)^n)[1, 1]: seq (a(n), n=0..33); # Alois P. Heinz, Jul 31 2008 MATHEMATICA CoefficientList[(1+3*x^2)/((1-x)^7*(1+x)^3) + O[x]^34, x] (* Jean-François Alcover, Jun 08 2015 *) LinearRecurrence[{4, -3, -8, 14, 0, -14, 8, 3, -4, 1}, {1, 4, 16, 44, 110, 236, 472, 868, 1519, 2520}, 34] (* Ray Chandler, Sep 23 2015 *) PROG (PARI) A018210(n)=(n+2)*(n+4)*(n+6)^2*(n^2+3*n+5)/1440-if(n%2, (n^2+7*n+11)/32) \\ M. F. Hasler, May 02 2009 CROSSREFS Sequence in context: A259013 A212960 A217873 * A054498 A217553 A225379 Adjacent sequences:  A018207 A018208 A018209 * A018211 A018212 A018213 KEYWORD nonn AUTHOR N. J. A. Sloane, Winston C. Yang (yang(AT)math.wisc.edu) STATUS approved

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Last modified December 4 13:27 EST 2016. Contains 278750 sequences.