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A210974
Decimal expansion of the angle (in degrees) between an edge and (the normal of) a face of the regular tetrahedron.
3
5, 4, 7, 3, 5, 6, 1, 0, 3, 1, 7, 2, 4, 5, 3, 4, 5, 6, 8, 4, 6, 2, 2, 9, 9, 9, 6, 6, 9, 9, 8, 1, 2, 1, 7, 9, 8, 1, 5, 0, 3, 4, 2, 1, 5, 5, 0, 4, 5, 3, 9, 7, 4, 1, 4, 4, 0, 8, 5, 5, 5, 3, 1, 7, 8, 0, 1, 9, 8, 7, 3, 2, 1, 9, 0
OFFSET
2,1
COMMENTS
Also known as "magic angle", the angle t such that 3*(cos t)^2 - 1 = 0.
See more comments in A195696. - Stanislav Sykora, Nov 14 2013
LINKS
C. O. Horgan and J. G. Murphy, On an angle with magical properties, Notices Amer. Math. Soc., 69:1 (2022), 22-25.
Wikipedia, Tetrahedron
Wikipedia, Magic angle
FORMULA
A195696 times 180 divided by Pi, see A072097.
EXAMPLE
54.7356103172453... degrees.
MATHEMATICA
RealDigits[t/.FindRoot[3Cos[t Degree]^2-1==0, {t, 54}, WorkingPrecision-> 120]][[1]] (* Harvey P. Dale, May 02 2014 *)
PROG
(PARI) acos(sqrt(1/3))*180/Pi \\ Charles R Greathouse IV, Nov 05 2017
CROSSREFS
Cf. A195696 (in radians).
Sequence in context: A293380 A358663 A021870 * A177161 A154776 A188932
KEYWORD
nonn,cons
AUTHOR
Omar E. Pol, Jul 17 2012
STATUS
approved