The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A213680 a(n) = 2*a(n-1)^2/3-3 with a(0)=6. 0
 6, 21, 291, 56451, 2124476931, 3008934820234119171, 6035792501611554034238453484153151491, 24287194081673507672666338605180770497437885188248737771493963111463682051 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS FORMULA a(n) = 3*cosh(2^n*arccosh(2)). a(n) = 3*A002812(n). [Giovanni Resta, Mar 04 2013] EXAMPLE a(1) = 2*a(0)^2/3-3 = 2*6^2/3-3 = 21, a(2) = 2*a(1)^2/3-3 = 2*21^2/3-3 = 291, a(3) = 2*a(2)^2/3-3 = 2*291^2/3-3 = 2*84681/3-3 = 56451. Or, by the first formula: a(3) = 3*cosh(2^3*arccosh(2)) = 56451, a(4) = 3*cosh(2^4*arccosh(2)) = 2124476931. PROG (Sage) var('x') p=2*x^2/3-3 s=[6] for i in [0..8]:     s=s+[p(s[i])] show(s) CROSSREFS Cf. A002812. Sequence in context: A131960 A244299 A143049 * A164643 A190275 A261844 Adjacent sequences:  A213677 A213678 A213679 * A213681 A213682 A213683 KEYWORD nonn AUTHOR Jose Eduardo Blazek, Mar 04 2013 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 9 21:08 EDT 2022. Contains 356026 sequences. (Running on oeis4.)