A062789 - OEIS

A062789

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

1, 2, 3, 2, 5, 6, 7, 4, 3, 10, 11, 4, 13, 14, 3, 8, 17, 6, 19, 4, 3, 22, 23, 24, 5, 26, 9, 4, 29, 6, 31, 16, 3, 34, 5, 12, 37, 38, 3, 8, 41, 6, 43, 4, 15, 46, 47, 16, 7, 10, 3, 4, 53, 18, 5, 8, 3, 58, 59, 4, 61, 62, 9, 32, 1, 6, 67, 4, 3, 10, 71, 24, 73, 74, 5, 4, 1, 6, 79, 16, 27, 82, 83, 12

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

OFFSET

1,2

LINKS

Harry J. Smith, Table of n, a(n) for n = 1..2000

MATHEMATICA

Table[GCD[n, EulerPhi[n]*(EulerPhi[n] + 1)], {n, 75}] (* Stefan Steinerberger, Apr 03 2006 *)

ep[n_]:=Module[{epn=EulerPhi[n]}, GCD[n, epn(epn+1)]]; Array[ep, 90] (* Harvey P. Dale, Jun 23 2011 *)

PROG

(PARI) for (n=1, 2000, p=eulerphi(n); write("b062789.txt", n, " ", gcd(n, p*(p + 1)))) \\ Harry J. Smith, Aug 11 2009

(Haskell)

a062789 n = gcd n (phi * (phi + 1)) where phi = a000010 n