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%I #32 Sep 14 2021 17:37:15
%S 1,1,2,2,3,3,4,4,4,4,4,5,5,5,5,5,5,5,6,6,6,6,6,6,6,6,6,6,6,6,6,7,7,7,
%T 7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
%U 8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,9,9,9,9,9,9,9,9
%N a(n) = floor(log_2(prime(n))).
%C a(n) is the greatest k such that 2^k does not exceed prime(n). - _David James Sycamore_, Sep 14 2021
%H T. D. Noe, <a href="/A098388/b098388.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n) = A000523(A000040(n)); A098391(n) = A000523(a(n)).
%F a(n) = A035100(n) - 1. - _Michel Marcus_, Sep 17 2017
%p map(ilog2, select(isprime,[2,seq(2*i+1,i=1..1000)])); # _Robert Israel_, Jun 08 2015
%t Floor[Log[2, Prime[Range[105]]]] (* data *) (* parameter changed by _Hartmut F. W. Hoft_, Jun 02 2015 *)
%o (PARI) a(n) = logint(prime(n), 2); \\ _Michel Marcus_, Sep 17 2017
%Y Cf. A000040, A000523, A023196, A035100, A098391.
%K nonn,easy
%O 1,3
%A _Reinhard Zumkeller_, Sep 06 2004
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