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Number of paraffins.
(Formerly M1740)
1

%I M1740 #40 Oct 13 2024 13:37:05

%S 1,2,7,14,29,48,79,116,169,230,311,402,517,644,799,968,1169,1386,1639,

%T 1910,2221,2552,2927,3324,3769,4238,4759,5306,5909,6540,7231,7952,

%U 8737,9554,10439,11358,12349,13376,14479,15620,16841,18102,19447,20834,22309

%N Number of paraffins.

%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

%H Vincenzo Librandi, <a href="/A005998/b005998.txt">Table of n, a(n) for n = 1..1000</a>

%H F. Javier de Vega, <a href="https://arxiv.org/abs/2003.13378">An extension of Furstenberg's theorem of the infinitude of primes</a>, arXiv:2003.13378 [math.NT], 2020.

%H S. M. Losanitsch, <a href="http://dx.doi.org/10.1002/cber.189703002144">Die Isomerie-Arten bei den Homologen der Paraffin-Reihe</a>, Chem. Ber. 30 (1897), 1917-1926.

%H S. M. Losanitsch, <a href="/A000602/a000602_1.pdf">Die Isomerie-Arten bei den Homologen der Paraffin-Reihe</a>, Chem. Ber. 30 (1897), 1917-1926. (Annotated scanned copy)

%H <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (2, 1, -4, 1, 2, -1).

%F G.f.: x*(x^4+2*x^3+2*x^2+1)/(-1+x)^2/(-1+x^2)^2.

%p a:= n-> (Matrix([[0, -1, -4, -11, -22, -41]]). 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]:

%p seq(a(n), n=1..38); # _Alois P. Heinz_, Jul 31 2008

%t a[n_] := 1/8*(2*n^3-2*n^2+5*n-(-1)^n*(n+1)+1); Array[a, 40] (* _Jean-François Alcover_, Mar 13 2014 *)

%t CoefficientList[Series[(x^4 + 2 x^3 + 2 x^2 + 1)/(-1 + x)^2/(-1 + x^2)^2, {x, 0, 40}], x] (* _Vincenzo Librandi_, Mar 15 2014 *)

%t LinearRecurrence[{2,1,-4,1,2,-1},{1,2,7,14,29,48},50] (* _Harvey P. Dale_, Oct 13 2024 *)

%o (Magma) [1/8*(2*n^3-2*n^2+5*n-(-1)^n*(n+1)+1): n in [1..50]]; // _Vincenzo Librandi_, Mar 15 2014

%K nonn,easy

%O 1,2

%A _N. J. A. Sloane_

%E More terms from _Vincenzo Librandi_, Mar 15 2014