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 A308632 Largest aggressor for the maximum number of peaceable coexisting queens as given in A250000. 1
 0, 0, 2, 3, 4, 6, 7, 10, 12, 15, 19 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Sequence A250000 is the maximum number m such that m white queens and m black queens can coexist on an n X n chessboard without attacking each other. However one of the players can have more than m queens, being a bigger 'aggressor' in peaceful times. The current sequence lists the largest aggressors with k queens when the opponent has m queens for an n X n chessboard (from A250000). The idea and name of the sequence was first mentioned by Bob Selcoe on May 29 2019 in the comment section of A250000. The sequence was initially generated by Roy van Rijn using a SAT solver and is optimal for n=1 to n=11 (as of June 12 2019). Bob Selcoe has shown it is possible to construct a 15 X 15 board with 32 queens of one color and 34 of another but this hasn't yet been proven to be optimal. Many of these values have already been obtained by Stephen Ainley in 1977 (see links). Conjecture: a(n) - A250000(n) <= 2 for all n. - Dmitry Kamenetsky, Oct 14 2019 LINKS Stephen Ainley, Mathematical Puzzles, London: G Bell & Sons, 1977. [Annotated scan of a portion of page 32] Dmitry Kamenetsky, Best known solutions for 12 <= n <= 30. FORMULA a(n) >= A250000(n). EXAMPLE Examples (omitted cases where the largest aggressor is equal to A250000): n=1: white queens 0, black queens 0 n=2: white queens 0, black queens 0 n=3: white queens 1, black queens 2 n=4: white queens 2, black queens 3 +-------+ |. W . W| |. . . .| |B . B .| |. . B .| +-------+ n=5: white queens 4, black queens 4 n=6: white queens 5, black queens 6 +-----------+ |. W . . . .| |W . W . . .| |. . . . B B| |. . . B . B| |W W . . . .| |. . . B . B| +-----------+ n=7: white queens 7, black queens 7 n=8: white queens 9, black queens 10 +---------------+ |. . . B B B . .| |W W . . . . . .| |. . . B . . . B| |. . . . . . B B| |. . . . . B B B| |. W W . . . . .| |W W W . . . . .| |W W . . . . . .| +---------------+ n=9: white queens 12, black queens 12 n=10: white queens 14, black queens 15 +-------------------+ |. . B B . . . . B B| |. . B B . . . B B B| |. . B . . . . B B B| |. . . . . . . B B .| |. W . . . . . . . .| |W W . . . . . . . .| |W W . . . . . . . .| |W . . . . W W . . .| |. . . . W W W . . .| |. . . . W W W . . .| +-------------------+ n=11: white queens 17, black queens 19 +---------------------+ |W . W . . . . . W . W| |. . . . B B B . . . .| |W . W . . . . . W . W| |. . . . B . B . . . .| |. B . . . B . B . B .| |. B . . B . B . . B .| |. B . . . B . B . B .| |. . . . B . B . . . .| |W . W . . . . . W . W| |. . . W . . . . . . .| |W . W . . . . . W . W| +---------------------+ CROSSREFS Cf. A250000. Sequence in context: A091515 A036405 A051424 * A137606 A320224 A328172 Adjacent sequences:  A308629 A308630 A308631 * A308633 A308634 A308635 KEYWORD nonn,hard,more AUTHOR Roy van Rijn, Jun 12 2019 STATUS approved

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Last modified August 6 16:05 EDT 2020. Contains 336255 sequences. (Running on oeis4.)