OFFSET
0,1
COMMENTS
Icosahedron: A three-dimensional figure with 20 equilateral triangle faces, 12 vertices, and 30 edges.
REFERENCES
Jan Gullberg, Mathematics from the Birth of Numbers, W. W. Norton & Co., NY & London, 1997, ยง12.4 Theorems and Formulas (Solid Geometry), p. 451.
LINKS
Ivan Panchenko, Table of n, a(n) for n = 0..1000
Dr. Math, Icosahedron.
Wikipedia, Icosahedron.
MathWorld, Icosahedron.
FORMULA
Equals sqrt(42 + 18*sqrt(5))/12.
EXAMPLE
0.75576131407617073048013370202500139263844478889356105922958289203910...
MATHEMATICA
RealDigits[(Sqrt[42+18Sqrt[5]]/12), 10, 175][[1]]
PROG
(PARI) sqrt((7+3*sqrt(5))/6)/2 \\ Stefano Spezia, Jan 27 2025
CROSSREFS
KEYWORD
AUTHOR
Vladimir Joseph Stephan Orlovsky, Jul 09 2010
EXTENSIONS
Partially rewritten by Charles R Greathouse IV, Feb 03 2011
STATUS
approved