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A071578
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Number of iterations of Pi(n) needed to reach 1, where Pi(x) denotes the number of primes <= x.
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0
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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, 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, 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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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FORMULA
| a(n) = a(Pi(n))+1.
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PROG
| (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, ", "); ); ))
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CROSSREFS
| Cf. A000720.
Sequence in context: A077463 A084556 A084506 * A157791 A156874 A078767
Adjacent sequences: A071575 A071576 A071577 * A071579 A071580 A071581
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KEYWORD
| easy,nonn
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AUTHOR
| Benoit Cloitre (benoit7848c(AT)orange.fr), May 31 2002
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