A330034 a(n) = sign(cos(n)).

1, 1, -1, -1, -1, 1, 1, 1, -1, -1, -1, 1, 1, 1, 1, -1, -1, -1, 1, 1, 1, -1, -1, -1, 1, 1, 1, -1, -1, -1, 1, 1, 1, -1, -1, -1, -1, 1, 1, 1, -1, -1, -1, 1, 1, 1, -1, -1, -1, 1, 1, 1, -1, -1, -1, 1, 1, 1, 1, -1, -1, -1, 1, 1, 1, -1, -1, -1, 1, 1, 1, -1, -1, -1, 1, 1, 1, -1

Offset

0

Comments

Also sign(sec(n)).

Links

Table of n, a(n) for n=0..77.

Formula

a(n) = -1 if 1/4 < {n/(2*Pi)} < 3/4, +1 if n = 0 or 0 < {n/(2*Pi)} < 1/4 or 3/4 < {n/(2*Pi)} < 1, where {} is the fractional part.

Mathematica

a[n_] := Sign[Cos[n]]; Array[a, 100, 0]

Prog

(PARI) a(n) = sign(cos(n))

Crossrefs

Cf. A057427 (sign), A070747 (sign(sin(n)) or sign(csc(n))), A330035 (sign(tan(n)) or sign(cot(n))), A131503 (indices of +1), A246444 (indices of -1).

Sequence in context: A156734 A119664 A257075 * A010555 A108784 A127252

Adjacent sequences: A330031 A330032 A330033 * A330035 A330036 A330037

Keyword

sign,easy

Author

Jianing Song, Nov 27 2019

Status

approved