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 A006317 Maximum number of chess queens of 3 colors on an n X n board such that no queen attacks or protects another queen of its color. (Formerly M2631) 0
 1, 3, 7, 12, 19, 27, 37, 46, 58, 71, 86, 102, 121, 137, 157, 178, 201, 225, 253, 276, 304, 334, 364 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Does the density approach a limit? REFERENCES N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Jon Perry, kQueens B. Recamán, Chess queens, Problem 89-8, Math. Intellig., 12 (No. 3, 1990), 65-68. EXAMPLE Examples to illustrate a(10) and a(11) (1,2,3 are colors; 0 is an empty square): 1213121213 3002000302 2131302103 3020010321 2013230103 1320010201 2001323132 3132010201 2001030103 1323212321 and 12123212123 30001003001 21232321232 30010003001 12323212123 30010030001 21232121232 30010030010 12323212323 30010030010 21232121232 Examples to illustrate a(12)-a(14) (1,2,3 are colors; 0 is an empty square); a(12) = 102: 121312131213 300203020302 213102010201 302031323132 201020010201 132313230103 201020102321 103010301003 321232123212 103010301030 201020102010 132313231323 a(13) = 121: 1232313121213 3001002003002 2123231312131 3001002003002 1232313121213 3001002003002 2123231312131 3001002003002 1232313121213 3001002003002 2123231312131 3001002003002 1232313121213 a(14) = 137: 12131212323132 30020030010201 21313121230103 30020030012321 12131212300103 30020030123201 21313120300102 30020031212301 12131200300102 30020312123231 21310003001002 30203121232313 20102003001002 13231312123231 CROSSREFS Sequence in context: A324125 A212293 A194102 * A194147 A077043 A022330 Adjacent sequences:  A006314 A006315 A006316 * A006318 A006319 A006320 KEYWORD nonn,more AUTHOR EXTENSIONS a(9) from Jud McCranie, Jun 01 2003 a(10) >= 69. - Jud McCranie, Jun 08 2003 Edited by Jud McCranie, Jun 01 2003 a(10) and a(11) from Tim Peters (tim.one(AT)comcast.net), Oct 15 2004, using a Python program a(12)-a(14) from Tim Peters (tim.one(AT)comcast.net), Nov 12 2004 a(15)-a(23) from Tim Peters (tim.one(AT)comcast.net), Oct 17 2006 STATUS approved

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Last modified July 20 22:20 EDT 2019. Contains 325189 sequences. (Running on oeis4.)