

A011764


a(n) = 3^(2^n) (or: write in base 3, read in base 9).


17




OFFSET

0,1


COMMENTS

a(n) is the secondhighest value k such that A173419(k) = n+2.  Charles R Greathouse IV, Oct 03 2012
Let b(0) = 6; b(n+1) = smallest number such that b(n+1) + Product_{i=0..n} b(i) divides b(n+1)*Product_{i=0..n} b(i). Then b(n+1) = a(n) for n >= 0.  Derek Orr, Dec 13 2014
Changing "+" to "": Let b(0) = 6; b(n+1) = smallest number such that b(n+1)  Product_{i=0..n} b(i) divides b(n+1)*Product_{i=0..n} b(i). Then b(n+2) = a(n) for n >= 0.  Derek Orr, Jan 04 2015
With offset = 1, a(n) is the number of collections C of subsets of {1,2,...,n} such that if S is in C then the complement of S is not in C.  Geoffrey Critzer, Feb 06 2017


LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..11


FORMULA

a(0)=3 and a(n+1) = a(n)^2.  Benoit Jubin, Jun 27 2009


MATHEMATICA

3^(2^Range[0, 10]) (* Harvey P. Dale, Oct 14 2012 *)


PROG

(MAGMA) [3^(2^n): n in [0..8]]; // Vincenzo Librandi, Sep 15 2011
(PARI) a(n)=3^2^n \\ Charles R Greathouse IV, Oct 03 2012


CROSSREFS

Sequence in context: A216206 A038062 A218149 * A018624 A274032 A032078
Adjacent sequences: A011761 A011762 A011763 * A011765 A011766 A011767


KEYWORD

nonn,easy


AUTHOR

Stephan Y Solomon (ilans(AT)way.com)


STATUS

approved



