A005997 Number of paraffins.
1, 3, 10, 20, 39, 63, 100, 144, 205, 275, 366, 468, 595, 735, 904, 1088, 1305, 1539, 1810, 2100, 2431, 2783, 3180, 3600, 4069, 4563, 5110, 5684, 6315, 6975, 7696, 8448, 9265, 10115, 11034, 11988, 13015, 14079, 15220, 16400, 17661, 18963, 20350, 21780, 23299
Offset: 1
References
- S. M. Losanitsch, Die Isomerie-Arten bei den Homologen der Paraffin-Reihe, Chem. Ber. 30 (1897), 1917-1926.
- N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
Links
- Enrique Pérez Herrero, Table of n, a(n) for n = 1..5000
- M. Golafshan, M. Rigo, and M. Whiteland, Computing the k-binomial complexity of generalized Thue-Morse words, arXiv:2412.18425 [math.CO], 2024. See p. 29.
- S. M. Losanitsch, Die Isomerie-Arten bei den Homologen der Paraffin-Reihe, Chem. Ber. 30 (1897), 1917-1926. (Annotated scanned copy)
- Index entries for linear recurrences with constant coefficients, signature (2,1,-4,1,2,-1).
Crossrefs
Cf. A005999.
Programs
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Maple
a:= n-> (Matrix([[0, 0, -1, -5, -12, -26]]). Matrix(6, (i, j)-> if (i=j-1) then 1 elif j=1 then [2, 1, -4, 1, 2, -1][i] else 0 fi)^n)[1, 1]: seq (a(n), n=1..50); # Alois P. Heinz, Jul 31 2008
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Mathematica
A005997[n_]:=1+Floor[(n-1)/2]+2*(Binomial[n+1,3]-Binomial[Floor[(n+1)/2],3]-Binomial[Ceiling[(n+1)/2],3]); Array[A005997,37] (* Enrique Pérez Herrero, Apr 22 2012 *) LinearRecurrence[{2, 1, -4, 1, 2, -1}, {1, 3, 10, 20, 39, 63}, 37] (* Bruno Berselli, Apr 22 2012 *)
Formula
G.f.: (x^3+3*x^2+x+1)*x / ((-1+x)^2*(-1+x^2)^2).
a(n) = A005999(n) + (n-1)^2. - Enrique Pérez Herrero, Mar 27 2012
a(n) = 1 + floor((n-1)/2) + 2*(C(n+1,3)-C(floor((n+1)/2),3)-C(ceiling((n+1)/2),3)). - Enrique Pérez Herrero, Apr 22 2012
a(n) = (n+1)*(2*n^2-(-1)^n+1)/8. - Bruno Berselli, Apr 22 2012
E.g.f.: (x*(3 + 4*x + x^2)*cosh(x) + (1 + 2*x + 4*x^2 + x^3)*sinh(x))/4. - Stefano Spezia, Dec 13 2021