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 A339819 #5 Dec 22 2020 18:30:07 %S A339819 2,3,5,7,11,13,17,19,23,29,31,33,37,41,43,47,53,59,61,67,69,71,73,79, %T A339819 83,89,97,101,103,107,109,113,127,131,137,139,141,145,149,151,157,163, %U A339819 167,173,177,179,181,191,193,197,199,211,213,217,223,227,229,233,239,241,249,251,253,257,263,269,271,277,281,283 %N A339819 Squarefree numbers k > 1 for which neither 2-adic nor 3-adic valuation of phi(k) exceeds the corresponding valuation of k-1. %H A339819 Antti Karttunen, <a href="/A339819/b339819.txt">Table of n, a(n) for n = 1..15620</a> %o A339819 (PARI) isA339819(n) = ((n>1)&&issquarefree(n)&&(valuation(eulerphi(n),2)<=valuation(n-1,2))&&(valuation(eulerphi(n),3)<=valuation(n-1,3))); %Y A339819 Cf. A000010, A005117, A007814, A007949. %Y A339819 Subsequence of A339817. %K A339819 nonn %O A339819 1,1 %A A339819 _Antti Karttunen_, Dec 20 2020