OFFSET
4,1
COMMENTS
An upper bound on the crossing number of the locally twisted n-dimensional hypercube LTQ(n). From Wang, p. 3. A lower bound is given in A188162 (may not be meaningful for n<4).
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.
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
EXAMPLE
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.
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 *)
PROG
(PARI) a(n)=floor((265/6)*(4^(n-4))-(n^2 + ((15+(-1)^(n-1))/6)*(2^(n-3))))
(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
CROSSREFS
Cf. A188162.
KEYWORD
nonn,easy
AUTHOR
Jonathan Vos Post, Mar 23 2011
EXTENSIONS
More terms from Franklin T. Adams-Watters, Mar 24 2011
More terms from Sean A. Irvine, May 24 2011
STATUS
approved