A143973 - OEIS

A143973

Distances between multiples of 3 in A000010.

2, 4, 1, 4, 1, 2, 5, 1, 1, 3, 4, 1, 1, 1, 1, 3, 1, 2, 4, 3, 2, 2, 1, 4, 1, 1, 2, 2, 3, 2, 1, 1, 2, 1, 1, 1, 2, 3, 2, 4, 1, 2, 2, 2, 1, 1, 4, 1, 1, 3, 1, 2, 1, 2, 3, 2, 3, 2, 2, 1, 2, 1, 3, 1, 1, 4, 1, 3, 1, 2, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 5, 1, 2, 1

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

Inspired by the question: is n == 1 mod phi(n) for n composite?

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

FORMULA

a(1) = 2 since the first two numbers k such that 3 | phi(k) are 7 and 9, and 9 - 7 = 2.

MATHEMATICA

Differences @ Position[EulerPhi[Range[200]], _?(Divisible[#, 3] &)] // Flatten (* Amiram Eldar, Feb 29 2020 *)

CROSSREFS