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A030179
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Quarter-squares squared: A002620^2.
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18
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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
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OFFSET
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0,4
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COMMENTS
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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
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REFERENCES
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C. Thomassen, Embeddings and minors, pp. 301-349 of R. L. Graham et al., eds., Handbook of Combinatorics, MIT Press.
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LINKS
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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).
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FORMULA
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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
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MATHEMATICA
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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 *)
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PROG
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(PARI) a(n) = (n^2\4)^2 \\ Charles R Greathouse IV, Jun 11 2015
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CROSSREFS
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Cf. A000241, A002620, A014540.
Sequence in context: A063755 A166721 A085040 * A207025 A207170 A207069
Adjacent sequences: A030176 A030177 A030178 * A030180 A030181 A030182
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KEYWORD
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nonn,easy
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AUTHOR
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N. J. A. Sloane, Jan 10 2002
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STATUS
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approved
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