A058515 - OEIS

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A058515

GCD of totients of consecutive integers.

1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 4, 6, 2, 8, 8, 2, 6, 2, 4, 2, 2, 2, 4, 4, 6, 6, 4, 4, 2, 2, 4, 4, 8, 12, 12, 18, 6, 8, 8, 4, 6, 2, 4, 2, 2, 2, 2, 2, 4, 8, 4, 2, 2, 8, 12, 4, 2, 2, 4, 30, 6, 4, 16, 4, 2, 2, 4, 4, 2, 2, 24, 36, 4, 4, 12, 12, 6, 2, 2, 2, 2, 2, 8, 2, 14, 8, 8, 8, 24, 4, 4, 2, 2, 8, 32, 6

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OFFSET

1,3

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = gcd(Phi(n+1), Phi(n)), where Phi = A000010.

EXAMPLE

n=61, gcd(Phi(62), Phi(61)) = gcd(30, 60) = 30, so a(61)=30.

MATHEMATICA

Map[GCD @@ # &, Partition[EulerPhi@ Range@ 98, 2, 1]] (* Michael De Vlieger, Aug 22 2017 *)

PROG