cp's OEIS Frontend

A163400 Number of bits in binary expansion of n-th nonprime.

%I A163400 #13 Mar 02 2018 02:11:46
%S A163400 1,1,3,3,4,4,4,4,4,4,5,5,5,5,5,5,5,5,5,5,5,6,6,6,6,6,6,6,6,6,6,6,6,6,
%T A163400 6,6,6,6,6,6,6,6,6,6,6,6,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
%U A163400 7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,8,8,8,8,8,8,8,8
%N A163400 Number of bits in binary expansion of n-th nonprime.
%C A163400 Here n-th nonprime=A141468(n).
%C A163400 For n > 2, a(n) = A029837(n) or A029837(n)+1.
%H A163400 J. Mulder, <a href="/A163400/b163400.txt">Table of n, a(n) for n = 1..90409</a>
%e A163400 a(1)=1(0=nonprime(1) written in base 2 and 10); a(2)=1(1=nonprime(2) written in base 2 and 10); a(3)=3(100=nonprime(3) written in base 2 where 4=nonprime(3) written in base 10).
%p A163400 A141468 := proc(n) option remember; if n = 1 then 0; else for a from procname(n-1)+1 do if not isprime(a) then return a; fi; od: fi; end: A070939 := proc(n) max(1,ilog2(n)+1) ; end: A163400 := proc(n) A070939(A141468(n)) ; end: seq(A163400(n),n=1..120) ; # _R. J. Mathar_, Oct 10 2009
%t A163400 Prepend[Flatten@ Array[If[PrimeQ[ # ], {}, IntegerLength[ #, 2]] &, 100000], 1] (* Jasper Mulder (jasper.mulder(AT)planet.nl), Jun 03 2010 *)
%Y A163400 Cf. A035100, A141468.
%K A163400 nonn,easy,base
%O A163400 1,3
%A A163400 _Juri-Stepan Gerasimov_, Jul 26 2009
%E A163400 Edited by _Charles R Greathouse IV_, Mar 22 2010