A230864 log2*(n) (version 3): number of iterations log_2(log_2(log_2(...(n)...))) required for the result to be <= 1.

0, 1, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4

Offset

1,3

Comments

This is the definition of log2* as given by Wikipedia on Nov 03 2013.

If a(n) = k, then n = 2^2^2^...^2^x, where x is in the range 0 < x <= 1 and there are k 2's in the tower. For example a(5)=3 and 5 = 2^2^2^.28134014520...

Links

Table of n, a(n) for n=1..80.

Wikipedia, Iterated Logarithm

Formula

a(1)=0; thereafter a(n) = A010096(n-1).

Crossrefs

Cf. A010096 (version 1), A001069 (version 2).

Sequence in context: A211020 A157639 A010096 * A063510 A156878 A214454

Adjacent sequences: A230861 A230862 A230863 * A230865 A230866 A230867

Keyword

nonn

Author

N. J. A. Sloane, Nov 03 2013

Status

approved