A079695 Values never taken by phi(j)/2 for any j: a(n) = A005277(n)/2.

7, 13, 17, 19, 25, 31, 34, 37, 38, 43, 45, 47, 49, 57, 59, 61, 62, 67, 71, 73, 76, 77, 79, 85, 87, 91, 93, 94, 97, 101, 103, 107, 109, 115, 117, 118, 121, 122, 123, 124, 127, 129, 133, 137, 139, 142, 143, 145, 149, 151, 152, 154, 157, 159

Offset: 1

Author

Jon Perry, Jan 31 2003

Keywords

• nonn

Comments

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

Examples

			A005277(1)=14, therefore a(1)=7.
		

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A005277 (nontotients), A002180 (complementary sequence).

Programs

Haskell

import Data.List.Ordered (minus)
a079695 n = a079695_list !! (n-1)
a079695_list = [1..] `minus` a002180_list
-- Reinhard Zumkeller, Nov 22 2015

Mathematica

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 *)

PARI

is(n)=!istotient(2*n) \\ Charles R Greathouse IV, Mar 23 2015