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A209211 Numbers n such that n-1 and phi(n) are relatively prime. 8
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

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

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 &]

PROG

(Haskell)

a209211 n = a209211_list !! (n-1)

a209211_list = filter (\x -> (x - 1) `gcd` a000010 x == 1) [1..]

-- Reinhard Zumkeller, Mar 02 2013

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

CROSSREFS

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

Sequence in context: A284788 A323288 A322131 * A064676 A147819 A230201

Adjacent sequences:  A209208 A209209 A209210 * A209212 A209213 A209214

KEYWORD

nonn

AUTHOR

José María Grau Ribas, Mar 06 2012

STATUS

approved

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Last modified June 17 19:10 EDT 2019. Contains 324198 sequences. (Running on oeis4.)