A185098 a(n) = floor((265/6)*4^(n-4) - n^2 - ((15+(-1)^(n-1))/6)* 2^(n-3)).
23, 141, 652, 2735, 11168, 44975, 180508, 722823, 2893168, 11575127, 46307132, 185237279, 740974336, 2963930847, 11855822524, 47423422103, 189694082672, 758776856135, 3035108998684, 12140438093295, 48561758666176, 194247043054991
Offset: 4
Examples
a(4) = floor(((265 / 6) * (4^(4 - 4))) - ((4^2) + (((15 + ((-1)^(4 - 1))) / 6) * (2^(4 - 3))))) = floor(23.5) = 23. a(5) = floor(((265 / 6) * (4^(5 - 4))) - ((5^2) + (((15 + ((-1)^(5 - 1))) / 6) * (2^(5 - 3))))) = floor(141) = 141.
Links
- Vincenzo Librandi, Table of n, a(n) for n = 4..1000
- Haoli Wang, Xirong Xu, Yuansheng Yang, Bao Liu, Wenping Zheng and Guoqing Wang, The crossing number of locally twisted cubes, arXiv:1103.4227 [math.CO], Mar 22, 2011.
Crossrefs
Cf. A188162.
Programs
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Magma
[Floor((265/6)*(4^(n-4))-(n^2 + ((15+(-1)^(n-1))/6)*(2^(n-3)))): n in [4..30]]; // Vincenzo Librandi, Mar 25 2012
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Mathematica
Table[Floor[(265/6)*4^(n-4) - n^2 - ((15+(-1)^(n-1))/6)* 2^(n-3)], {n,4,50}] (* G. C. Greubel, Jun 22 2017 *) -
PARI
a(n)=floor((265/6)*(4^(n-4))-(n^2 + ((15+(-1)^(n-1))/6)*(2^(n-3))))
Formula
Empirical G.f.: -x^4*(8*x^6-36*x^5+22*x^4+67*x^3-82*x^2-20*x+23) / ((x-1)^3*(2*x-1)*(2*x+1)*(4*x-1)). - Colin Barker, Dec 04 2012
Extensions
More terms from Franklin T. Adams-Watters, Mar 24 2011
More terms from Sean A. Irvine, May 24 2011
Comments