A282160 Least k > 1 such that k*n is not a totient number.

3, 7, 3, 17, 3, 15, 2, 19, 3, 5, 3, 43, 2, 7, 3, 19, 2, 5, 2, 17, 3, 7, 3, 167, 2, 7, 3, 11, 3, 3, 2, 19, 3, 2, 3, 67, 2, 2, 3, 17, 3, 17, 2, 7, 2, 5, 2, 211, 2, 7, 3, 7, 3, 11, 3, 13, 2, 3, 2, 139, 2, 2, 3, 31, 3, 9, 2, 5, 3, 5, 2, 109, 2, 5, 3, 2, 2, 3, 2, 85, 3, 3, 3, 61

Offset

1,1

Comments

First occurrence of odd k or zero if impossible: 0, 1, 10, 2, 66, 28, 56, 6, 4, 8, 5244, 460, 272, 0, 232, 64, 7788, 4180, 300, 348, 328, 12, etc. - Robert G. Wilson v, Feb 09 2017

Links

Altug Alkan, Table of n, a(n) for n = 1..10000

Formula

a(A079695(n)) = 2. - Michel Marcus, Feb 08 2017

Example

a(14) = 7 because 7 * 14 = 98 is not a totient number and 7 is the least number that is greater than 1 with this property.

Mathematica

TotientQ[m_] := Select[ Range[m +1, 2m*Product[(1 - 1/(k*Log[k]))^(-1), {k, 2, DivisorSigma[0, m]}]], EulerPhi[#] == m &, 1] != {}; (* after Jean-François Alcover, May 23 2011 in A002202 *) f[n_] := Block[{k = 2}, While[ TotientQ[k*n], k++]; k]; Array[f, 84] (* Robert G. Wilson v, Feb 09 2017 *)

Prog

(PARI) a(n) = my(k = 2); while (istotient(k*n), k++); k;

Crossrefs

Cf. A000010, A002202, A007617, A067005, A071615, A079695.

Sequence in context: A088837 A201385 A186107 * A338266 A019158 A367865

Adjacent sequences: A282157 A282158 A282159 * A282161 A282162 A282163

Keyword

nonn

Author

Altug Alkan, Feb 07 2017

Status

approved