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A225240
The squares on a chessboard that are white, counting from top left corner and down.
1
1, 3, 5, 7, 10, 12, 14, 16, 17, 19, 21, 23, 26, 28, 30, 32, 33, 35, 37, 39, 42, 44, 46, 48, 49, 51, 53, 55, 58, 60, 62, 64
OFFSET
1,2
COMMENTS
Equivalently it represents the squares that are black, counting from bottom left corner and up.
FORMULA
a(1) = 1, a(n) = a(n-1) + 2 + (mod(a(n-1)+1, 8) == 0) - (mod(a(n-1), 8) == 0).
To check if n is white: mod(s, 2) + (1 - 2*mod(s, 2)) * mod(floor((s-1)/8), 2).
MATHEMATICA
sqColor[n_] := Mod[n, 2] + (1 - 2*Mod[n, 2])*Mod[Floor[(n - 1)/8], 2]; Select[Range[64], sqColor[#] == 1 &]
CROSSREFS
Cf. A225773 (black-squares sequence).
Sequence in context: A108052 A359113 A046868 * A104309 A306683 A184586
KEYWORD
nonn,fini,full,easy
AUTHOR
Jonas Hallgren, Jul 25 2013
STATUS
approved