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 A334789 a(n) = 2^log_2*(n) where log_2*(n) = A001069(n) is the number of log_2(log_2(...log_2(n))) iterations needed to reach < 2. 2
 1, 2, 2, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Differs from A063511 for n>=256.  For example a(256)=8 whereas A063511(256)=16.  The respective exponent sequences are A001069 (for here) and A211667 (for A063511) which likewise differ for n>=256. 2^log*(n) arises in computational complexity measures for Fürer's multiplication algorithm. LINKS Kevin Ryde, Table of n, a(n) for n = 1..8192 Martin Fürer, Faster integer multiplication, Proceedings of the 39th Annual ACM Symposium on Theory of Computing, 11-13 June 2007.  And in SIAM Journal of Computing, volume 30, number 3, 2009, pages 979-1005. FORMULA a(n) = 2^A001069(n). a(n) = 2^lg*(n), where lg*(x) = 0 if x <= 1 and 1 + lg*(log_2(x)) otherwise. - Charles R Greathouse IV, Apr 09 2012 PROG (PARI) a(n)=my(t); while(n>1, n=log(n+.5)\log(2); t++); 2^t \\ Charles R Greathouse IV, Apr 09 2012 (PARI) a(n) = my(c=0); while(n>1, n=logint(n, 2); c++); 1<

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Last modified January 19 16:16 EST 2021. Contains 340270 sequences. (Running on oeis4.)