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 A063724 Consider problem of placing N queens on an n X n board so that each queen attacks precisely 4 others. Sequence gives maximal number of queens. 1
 0, 0, 0, 8, 11, 15, 18, 21, 24, 27, 30, 33, 36, 39, 42, 45, 48, 51, 54, 57, 60, 63, 66, 69, 72, 75, 78, 81, 84, 87, 90, 93, 96, 99, 102, 105, 108, 111, 114, 117, 120, 123, 126, 129, 132, 135, 138, 141, 144, 147, 150, 153, 156, 159, 162, 165, 168, 171, 174, 177, 180 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 REFERENCES Peter Hayes, A Problem of Chess Queens, Journal of Recreational Mathematics, 24(4), 1992, 264-271. LINKS FORMULA a(1)=a(2)=a(3)=0, a(4)=8, a(5)=11, a(n) = 3n - 3 for n >= 6. From Colin Barker, Apr 13 2012: (Start) a(n) = 2*a(n-1) - a(n-2) for n >= 8. G.f.: x^4*(8 - 5*x + x^2 - x^3)/(1-x)^2. (End) EXAMPLE Examples from Sean A. Irvine, Mar 31 2019: (Start) a(4) = 8: .QQ. Q..Q Q..Q .QQ. a(5) = 11: .Q.Q. Q...Q Q...Q Q...Q .QQQ. a(6) = 15: .Q..Q. Q...QQ Q.Q... Q....Q Q....Q .QQQQ. (End) CROSSREFS Cf. A051754-A051759, A051567-A051571, A019654. Sequence in context: A078117 A256073 A032423 * A317770 A154685 A068591 Adjacent sequences: A063721 A063722 A063723 * A063725 A063726 A063727 KEYWORD easy,nonn AUTHOR Jud McCranie, Aug 11 2001 STATUS approved

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Last modified March 25 06:19 EDT 2023. Contains 361511 sequences. (Running on oeis4.)