A209211 Numbers n such that n-1 and phi(n) are relatively prime.

1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 54, 56, 58, 60, 62, 64, 68, 72, 74, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108, 110, 114, 116, 118, 120, 122, 126, 128, 132, 134, 136, 138

Offset: 1

Author

José María Grau Ribas, Mar 06 2012

Keywords

• nonn

Comments

A063994(a(n)) = 1. - Reinhard Zumkeller, Mar 02 2013

a(n) = A111305(n-2) for n >= 3. - Emmanuel Vantieghem, Jul 03 2013

n such that A049559(n) = 1. Includes A100484 and A000079. - Robert Israel, Nov 09 2015

All terms except the first one are even. Missing even terms are A039772. - Robert G. Wilson v, Sep 26 2016

Numbers n such that A187730(n) = 1. - Thomas Ordowski, Dec 29 2016

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000010, A000079, A003277, A039772, A049559, A063994, A100484, A111305.

Programs

Haskell

a209211 n = a209211_list !! (n-1)
a209211_list = filter (\x -> (x - 1) `gcd` a000010 x == 1) [1..]
-- Reinhard Zumkeller, Mar 02 2013

Maple

select(n -> igcd(n-1, numtheory:-phi(n)) = 1, [$1..1000]); # Robert Israel, Nov 09 2015

Mathematica

Select[Range[200], GCD[# - 1, EulerPhi[#]] == 1 &]

PARI

isok(n) = gcd(n-1, eulerphi(n)) == 1; \\ Michel Marcus, Sep 26 2016