login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A030179 Quarter-squares squared: A002620^2. 18
0, 0, 1, 4, 16, 36, 81, 144, 256, 400, 625, 900, 1296, 1764, 2401, 3136, 4096, 5184, 6561, 8100, 10000, 12100, 14641, 17424, 20736, 24336, 28561, 33124, 38416, 44100, 50625, 57600, 65536, 73984, 83521, 93636, 104976, 116964 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

Conjectured to be crossing number of complete bipartite graph K_{n,n}. Known to be true for n <= 7.

If the Zarankiewicz conjecture is true, then a(n) is also the rectilinear crossing number of K_{n,n}. - Eric W. Weisstein, Apr 24 2017

a(n+1) is the number of 4-tuples (w,x,y,z) with all terms in {0,...,n}, and w,x,y+1,z+1 all even. - Clark Kimberling, May 29 2012

REFERENCES

C. Thomassen, Embeddings and minors, pp. 301-349 of R. L. Graham et al., eds., Handbook of Combinatorics, MIT Press.

LINKS

Table of n, a(n) for n=0..37.

G. Xiao, Contfrac

Eric Weisstein's World of Mathematics, Complete Bipartite Graph

Eric Weisstein's World of Mathematics, Graph Crossing Number

Eric Weisstein's World of Mathematics, Rectilinear Crossing Number

Eric Weisstein's World of Mathematics, Zarankiewicz's Conjecture

Index entries for linear recurrences with constant coefficients, signature (2,2,-6,0,6,-2,-2,1).

FORMULA

a(n) = floor(n^2/4)^2.

G.f.: x^2*(1+2*x+6*x^2+2*x^3+x^4) / ( (1+x)^3*(1-x)^5 ). a(n) = +2*a(n-1) +2*a(n-2) -6*a(n-3) +6*a(n-5) -2*a(n-6) -2*a(n-7) +a(n-8). - R. J. Mathar, Jul 08 2010

a(n) = (2*n^4-2*n^2+1+(2*n^2-1)*(-1)^n)/32. - Luce ETIENNE, Aug 11 2014

MATHEMATICA

f[n_]:=Floor[n^2/2]; Table[Nest[f, n, 2], {n, 5!}]/2 (* Vladimir Joseph Stephan Orlovsky, Mar 10 2010 *)

LinearRecurrence[{2, 2, -6, 0, 6, -2, -2, 1}, {0, 0, 1, 4, 16, 36, 81, 144}, 6] (* Harvey P. Dale, Apr 26 2011 *)

Floor[Range[0, 30]^2/4]^2 (* Eric W. Weisstein, Apr 24 2017 *)

PROG

(PARI) a(n) = (n^2\4)^2 \\ Charles R Greathouse IV, Jun 11 2015

CROSSREFS

Cf. A000241, A002620, A014540.

Sequence in context: A063755 A166721 A085040 * A207025 A207170 A207069

Adjacent sequences:  A030176 A030177 A030178 * A030180 A030181 A030182

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, Jan 10 2002

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 22 18:55 EDT 2018. Contains 316500 sequences. (Running on oeis4.)