A213681 a(n) = a(n-1)^2/2 - 4 with a(0) = 6.

6, 14, 94, 4414, 9741694, 47450300994814, 1125765532249223239027447294, 633674016800188444301553476967536472012841942973961214

Offset: 0

Author

Jose Eduardo Blazek, Mar 04 2013

Keywords

• nonn

Comments

The next term has 108 digits. - Harvey P. Dale, Apr 21 2018

Examples

			a(2) = a(1)^2/2-4 = 14^2/2-4 = 94.
		

Crossrefs

Cf. A005248.

Programs

Mathematica

NestList[#^2/2-4&,6,8] (* Harvey P. Dale, Apr 21 2018 *)

Sage

var('x')
p=x^2/2-4
s=[6]
for i in [0..8]:
    s=s+[p(s[i])]
show(s)

Formula

a(n) = 4*cosh(2^n*arccosh(3/2)).

a(n) = 2*A005248(2^n). [Bruno Berselli, Mar 04 2013]