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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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1
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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
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OFFSET
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1,3
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LINKS
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FORMULA
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a(n) = a(Pi(n))+1.
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MATHEMATICA
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Table[Length[NestWhileList[PrimePi[#]&, n, #!=1&]]-1, {n, 110}] (* Harvey P. Dale, Dec 24 2018 *)
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PROG
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(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
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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