A144742 - OEIS

%I #20 Jan 30 2020 07:02:12

%S 5,7,11,17,23,29,37,41,47,53,59,67,71,79,83,89,97,107,113,127,131,137,

%T 149,157,163,167,173,179,191,197,211,223,227,239,251,257,263,269,277,

%U 281,293,307,311,317,331,337,347,359,367,373,379,383,389,397,401,409

%N Integers m such that phi(2, m) = A144740(m) > phi(2, k) for 0 < k < m.

%C Subset of the primes (A000040).

%C Except for 5 and 7, if one member of a twin prime pair is included, the other is not.

%H Amiram Eldar, <a href="/A144742/b144742.txt">Table of n, a(n) for n = 1..10000</a>

%t phi2[n_] := phi2[n] = Count[Range[n-1], _?(Total[Last /@ FactorInteger[#]] == 2 && CoprimeQ[#, n] &)];

%t Select[Range[300], And @@ Table[phi2[#] > phi2[k], {k, #-1}] &]

%t (* _Andrey Zabolotskiy_, Sep 09 2019 *)

%Y Cf. A000040, A001097, A144740.

%Y A005385 is a subsequence.

%K easy,nonn

%O 1,1

%A _Reikku Kulon_, Sep 20 2008