A225240 - OEIS

A225240

The squares on a chessboard that are white, counting from top left corner and down.

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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

COMMENTS

Equivalently it represents the squares that are black, counting from bottom left corner and up.

LINKS

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).

KEYWORD

nonn,fini,full,easy

AUTHOR

STATUS

approved