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 A053148 #23 May 31 2018 02:07:10
%S A053148 1,2,3,5,5,8,5,9,8,16,6,9,12,8,9,7,4,11,6,6,9,13,8,13,11,17,7,13,20,4,
%T A053148 11,11,15,13,9,19,13,6,4,13,4,4,8,4,24,20
%N A053148 When cototient function (A051953) is iterated with initial value A002110(n), a(n) = exponent of the largest power of 2 which appears in the iteration.
%C A053148 In these iteration chains, powers of 2 seem to be in the minority.
%C A053148 The sequence is not monotonic.
%e A053148 For n=10, the iteration chain of 43 terms is {6469693230, 5447823150, 4315810350, ..., 188416, 98304, 65536, 32768, ..., 4, 2, 1, 0} in which the largest power of 2 is 65536 = 2^16, so a(10)=16;
%e A053148 for n=11 the length is 61, including 54 numbers that are not powers of 2 and 7 powers of 2, of which the largest is 2^6 thus a(11)=6.
%t A053148 a[n_] := Max@ IntegerExponent[ NestWhileList[# - EulerPhi[#] &, Times @@ Prime[Range[n]], # > 1 &], 2]; Array[a, 25] (* _Giovanni Resta_, May 30 2018 *)
%o A053148 (PARI) A051953(n)= { return(n-eulerphi(n)); } A002110(n)= { return(prod(i=1,n,prime(i))); } ispow2(n)= { local(nbin,nbinl,sd); nbin=binary(n); nbinl=matsize(nbin); sd=sum(i=1,nbinl[2],nbin[i]); if(sd==1, return(nbinl[2]-1), return(0); ); } A053148itr(n)= { local(v,vbin,maxp); v=A002110(n); maxp=ispow2(v); while(v>0, v=A051953(v); maxp=max(maxp,ispow2(v)); ); return(maxp); } { for(n=1,70, print1(A053148itr(n),","); ); } \\ _R. J. Mathar_, May 19 2006
%Y A053148 Cf. A002110, A051953.
%K A053148 more,nonn
%O A053148 1,2
%A A053148 _Labos Elemer_, Feb 28 2000
%E A053148 More terms from _R. J. Mathar_, May 19 2006
%E A053148 a(37)-a(46) from _Giovanni Resta_, May 31 2018