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A209211 Numbers n such that n-1 and phi(n) are relatively prime. 10
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 September 24 21:35 EDT 2020. Contains 337322 sequences. (Running on oeis4.)