OFFSET
0,1
LINKS
E. B. Escott, Rapid method for extracting a square root, Amer. Math. Monthly, 44 (1937), 644-646.
FORMULA
a(n) = (4 + sqrt(15))^(3^n) + (4 - sqrt(15))^(3^n). - Bruno Berselli, Feb 10 2017
a(n) = -2*cos(3^n * arccos(-4)). - Daniel Suteu, Feb 10 2017
MATHEMATICA
RecurrenceTable[{a[0] == 8, a[n] == a[n-1]^3 - 3 a[n-1]}, a, {n, 8}]
PROG
(Magma) [n eq 1 select 8 else Self(n-1)^3 - 3*Self(n-1): n in [1..6]];
CROSSREFS
KEYWORD
nonn
AUTHOR
Vincenzo Librandi, Feb 10 2017
STATUS
approved