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 A079695 #21 Nov 22 2015 13:34:59
%S A079695 7,13,17,19,25,31,34,37,38,43,45,47,49,57,59,61,62,67,71,73,76,77,79,
%T A079695 85,87,91,93,94,97,101,103,107,109,115,117,118,121,122,123,124,127,
%U A079695 129,133,137,139,142,143,145,149,151,152,154,157,159
%N A079695 Values never taken by phi(j)/2 for any j: a(n) = A005277(n)/2.
%C A079695 Because the degree of the minimal polynomial of cos(2*Pi/k) is phi(k)/2, the degree can never be a number in this sequence. - _Artur Jasinski_, Feb 23 2011
%H A079695 Charles R Greathouse IV, <a href="/A079695/b079695.txt">Table of n, a(n) for n = 1..10000</a>
%e A079695 A005277(1)=14, therefore a(1)=7.
%t A079695 phiQ[m_] := Select[Range[m + 1, 2 m*Product[(1 - 1/(k*Log[k]))^(-1), {k, 2, DivisorSigma[0, m]}]], EulerPhi[#] == m &, 1] != {}; t = Select[Range[2, 320], phiQ]/2; Select[Range@ Max@ t, !MemberQ[t, #] &] (* _Michael De Vlieger_, Mar 22 2015, after _Jean-François Alcover_ at A002180 *)
%o A079695 (PARI) is(n)=!istotient(2*n) \\ _Charles R Greathouse IV_, Mar 23 2015
%o A079695 (Haskell)
%o A079695 import Data.List.Ordered (minus)
%o A079695 a079695 n = a079695_list !! (n-1)
%o A079695 a079695_list = [1..] `minus` a002180_list
%o A079695 -- _Reinhard Zumkeller_, Nov 22 2015
%Y A079695 Cf. A005277 (nontotients), A002180 (complementary sequence).
%K A079695 nonn
%O A079695 1,1
%A A079695 _Jon Perry_, Jan 31 2003