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A374933
Maximum number of squares covered (i.e., attacked) by 2 independent (i.e., non-attacking) queens on an n X n chessboard.
5
9, 15, 23, 30, 37, 44, 52, 60, 68, 76, 84, 92, 100, 108, 116, 124, 132, 140, 148, 156, 164, 172, 180, 188, 196, 204, 212, 220, 228, 236, 244, 252, 260, 268, 276, 284, 292, 300, 308, 316, 324, 332, 340, 348, 356, 364, 372, 380, 388, 396, 404, 412, 420
OFFSET
3,1
COMMENTS
It is not possible to place two non-attacking queens on a 1 X 1 or 2 X 2 chessboard.
FORMULA
a(n) = 8*n - 20 for n >= 8.
G.f.: x^3*(9 - 3*x + 2*x^2 - x^3 + x^6)/(1 - x)^2. - Stefano Spezia, Jul 25 2024
CROSSREFS
Cf. A017113, A047461 (case for one queen).
Sequence in context: A102739 A124622 A189051 * A274288 A172292 A075638
KEYWORD
nonn,easy
AUTHOR
John King, Jul 24 2024
STATUS
approved