%I #11 Dec 24 2020 21:22:47

%S 33,65,129,141,145,161,177,201,217,249,253,321,385,393,417,501,537,

%T 649,681,705,721,737,849,865,897,913,973,993,1041,1057,1081,1101,1121,

%U 1135,1149,1169,1177,1281,1329,1345,1401,1441,1457,1473,1497,1509,1537,1561,1569,1585,1633,1689,1729,1761,1793,1821,1837,1841

%N Odd squarefree numbers k > 1 for which bigomega(phi(k)) < bigomega(k-1), where bigomega gives the number of prime divisors, counted with multiplicity.

%C All terms can be found in A339911. Also, all nonmultiples of 3 certainly occur in A339912 also.

%C The first term of the form 4u+3 is 1135.

%H Antti Karttunen, <a href="/A339908/b339908.txt">Table of n, a(n) for n = 1..26693; all terms < 2^20</a>

%o (PARI) isA339908(n) = ((n>1)&&(n%2)&&issquarefree(n)&&(bigomega(eulerphi(n))<bigomega(n-1)));

%Y Cf. A000010, A001222.

%Y Subsequence of A056911 and of A339907, A339911.

%Y Cf. also A339912.

%Y Cf. A339909 (a subsequence).

%K nonn

%O 1,1

%A _Antti Karttunen_, Dec 21 2020