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A049586 a(n) is the GCD of the cototients (A051953) of n and n+1. 6
1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 5, 3, 1, 1, 1, 1, 3, 3, 1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 5, 1, 1, 1, 1, 3, 3, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 3, 3, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,9

COMMENTS

Most of the terms are 1.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..5000

FORMULA

a(n) = gcd(n + 1 - phi(n+1), n - phi(n)).

a(n) = gcd(A051953(n+1), A051953(n)).

MATHEMATICA

Map[GCD @@ Map[# - EulerPhi@ # &, #] &, Partition[Range@ 106, 2, 1]] (* Michael De Vlieger, Aug 09 2017 *)

PROG

(MAGMA) [GCD((n+1-EulerPhi(n+1)), n-EulerPhi(n)): n in [1..100]]; // Vincenzo Librandi, Aug 10 2017

CROSSREFS

Cf. A000010, A051953, A058515.

Sequence in context: A030578 A030577 A070670 * A133721 A083202 A030560

Adjacent sequences:  A049583 A049584 A049585 * A049587 A049588 A049589

KEYWORD

nonn

AUTHOR

Labos Elemer, Dec 28 2000

STATUS

approved

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Last modified September 26 23:47 EDT 2020. Contains 337378 sequences. (Running on oeis4.)