OFFSET
1,1
COMMENTS
Given a right circular cone with polar angle theta, the solid angle it subtends is 2*Pi(1-cos(theta)). Not to be confused with the area, in steradians, of a spherical square with the side theta (see A231986).
LINKS
Stanislav Sykora, Table of n, a(n) for n = 1..2000
Wikipedia, Solid angle
Wikipedia, Steradian
Wikipedia, Cone
FORMULA
2*Pi*(1-cos(1)) = 4*Pi*A243597.
EXAMPLE
2.8883657975136401375431217405500923198415259929590102...
MATHEMATICA
RealDigits[2 Pi (1 - Cos[1]), 10, 111][[1]] (* Robert G. Wilson v, Jun 12 2014 *)
PROG
(PARI) 2*Pi*(1-cos(1))
CROSSREFS
KEYWORD
AUTHOR
Stanislav Sykora, Jun 07 2014
STATUS
approved