This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A071578 #16 Sep 20 2024 15:37:40
%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,
%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,
%U A071578 5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5
%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.
%F A071578 a(n) = A060197(n) - 2. - _Filip Zaludek_, Dec 10 2016
%t A071578 Table[Length[NestWhileList[PrimePi[#]&,n,#!=1&]]-1,{n,110}] (* _Harvey P. Dale_, Dec 24 2018 *)
%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.
%K A071578 easy,nonn
%O A071578 1,3
%A A071578 _Benoit Cloitre_, May 31 2002