A015733 - OEIS

%I #46 May 15 2024 01:31:57

%S 2,4,6,12,14,16,20,22,25,27,32,36,38,42,44,46,48,50,54,60,62,64,66,68,

%T 75,80,81,86,92,94,96,100,112,114,116,118,121,132,134,138,142,144,150,

%U 154,158,160,162,164,166,180,186,188,189,192,196,200,204

%N Numbers k such that d(k) does not divide phi(k).

%H Michael De Vlieger, <a href="/A015733/b015733.txt">Table of n, a(n) for n = 1..18157</a> (first 2000 terms from Enrique Pérez Herrero)

%t Select[Range[204], ! Divisible[EulerPhi[#], DivisorSigma[0, #]] &]

%o (PARI) is(k) = {my(f = factor(k), d = numdiv(f), p = eulerphi(f)); p % d;} \\ _Amiram Eldar_, May 15 2024

%Y Cf. A000005 (d), A000010 (phi), A015734, A020491 (d(k) does divide phi(k)).

%K nonn

%O 1,1

%A _Robert G. Wilson v_