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 A230864 log2*(n) (version 3): number of iterations log_2(log_2(log_2(...(n)...))) required for the result to be <= 1. 5
 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 (list; graph; refs; listen; history; text; internal format)
 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 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

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Last modified January 25 01:49 EST 2020. Contains 331229 sequences. (Running on oeis4.)