A339819 - OEIS

%I #5 Dec 22 2020 18:30:07

%S 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 83,89,97,101,103,107,109,113,127,131,137,139,141,145,149,151,157,163,

%U 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 Squarefree numbers k > 1 for which neither 2-adic nor 3-adic valuation of phi(k) exceeds the corresponding valuation of k-1.

%H Antti Karttunen, <a href="/A339819/b339819.txt">Table of n, a(n) for n = 1..15620</a>

%o (PARI) isA339819(n) = ((n>1)&&issquarefree(n)&&(valuation(eulerphi(n),2)<=valuation(n-1,2))&&(valuation(eulerphi(n),3)<=valuation(n-1,3)));

%Y Cf. A000010, A005117, A007814, A007949.

%Y Subsequence of A339817.

%K nonn

%O 1,1

%A _Antti Karttunen_, Dec 20 2020