A049586 - OEIS

A049586

a(n) is the GCD of the cototients (A051953) of n and n+1.

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 *)