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 A339871 #6 Dec 20 2020 22:23:51 %S A339871 0,0,0,1,0,1,0,1,1,1,0,1,0,2,1,1,0,2,0,1,1,2,0,1,1,2,1,1,0,1,0,1,1,1, %T A339871 2,2,0,2,2,1,0,2,0,2,2,2,0,1,1,2,1,1,0,2,2,2,1,2,0,1,0,3,2,1,1,1,0,1, %U A339871 1,1,0,2,0,2,2,2,2,2,0,1,1,2,0,2,1,3,2,2,0,2,1,2,2,2,2,1,0,3,3,2,0,1,0,2,2 %N A339871 Number of primes p for which the p-adic valuation of phi(n) exceeds the p-adic valuation of n-1, with a(1) = 0 by convention. %H A339871 Antti Karttunen, <a href="/A339871/b339871.txt">Table of n, a(n) for n = 1..65537</a> %F A339871 a(n) = A001221(A160595(n)). %F A339871 a(n) <= A055734(n). %o A339871 (PARI) A339871(n) = if(1==n,0,my(s=0); for(k=1,n,my(p=prime(k)); if(valuation(eulerphi(n),p)>valuation(n-1,p), s++)); (s)); %o A339871 (PARI) A339871(n) = if(1==n,0,my(f=factor(eulerphi(n))); sum(i=1,#f~,f[i,2]>valuation(n-1,f[i,1]))); %o A339871 (PARI) A339871(n) = omega(eulerphi(n)/gcd(n-1,eulerphi(n))); %Y A339871 Cf. A001221, A055734, A160595, A339817, A339872. %K A339871 nonn %O A339871 1,14 %A A339871 _Antti Karttunen_, Dec 20 2020