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A213681
a(n) = a(n-1)^2/2 - 4 with a(0) = 6.
0
6, 14, 94, 4414, 9741694, 47450300994814, 1125765532249223239027447294, 633674016800188444301553476967536472012841942973961214
OFFSET
0,1
COMMENTS
The next term has 108 digits. - Harvey P. Dale, Apr 21 2018
FORMULA
a(n) = 4*cosh(2^n*arccosh(3/2)).
a(n) = 2*A005248(2^n). [Bruno Berselli, Mar 04 2013]
EXAMPLE
a(2) = a(1)^2/2-4 = 14^2/2-4 = 94.
MATHEMATICA
NestList[#^2/2-4&, 6, 8] (* Harvey P. Dale, Apr 21 2018 *)
PROG
(Sage)
var('x')
p=x^2/2-4
s=[6]
for i in [0..8]:
s=s+[p(s[i])]
show(s)
CROSSREFS
Cf. A005248.
Sequence in context: A200033 A219376 A130263 * A308489 A301425 A077401
KEYWORD
nonn
AUTHOR
Jose Eduardo Blazek, Mar 04 2013
STATUS
approved