Search: id:A071578
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%I A071578
%S A071578 0,1,2,2,3,3,3,3,3,3,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,5,5,5,5,5,
%T A071578 5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
%U A071578 5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5
%N A071578 Number of iterations of Pi(n) needed to reach 1, where Pi(x) denotes 
               the number of primes <= x.
%F A071578 a(n) = a(Pi(n))+1.
%o A071578 (PARI) for(n=2,150,s=n; t=0; while(s!=1,t++; s=sum(i=2,s,isprime(i)); 
               if(s==1,print1(t,","); ); ))
%Y A071578 Cf. A000720.
%Y A071578 Sequence in context: A077463 A084556 A084506 this_sequence A157791 A156874 
               A078767
%Y A071578 Adjacent sequences: A071575 A071576 A071577 this_sequence A071579 A071580 
               A071581
%K A071578 easy,nonn
%O A071578 1,3
%A A071578 Benoit Cloitre (benoit7848c(AT)orange.fr), May 31 2002

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