A071349 - OEIS

A071349

Numbers k for which the GCD of the k-th primorial number and its totient (A058250) sets record.

1, 2, 4, 5, 9, 10, 15, 16, 17, 23, 27, 28, 35, 39, 40, 41, 43, 49, 56, 57, 61, 62, 64, 66, 69, 72, 73, 76, 77, 91, 92, 96, 97, 102, 103, 104, 107, 111, 114, 117, 119, 127, 128, 137, 139, 143, 146, 150, 154, 155, 166, 171, 181, 182, 186, 195, 196, 201, 208, 214, 215

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

OFFSET

1,2

LINKS

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

FORMULA

If A058250(m) > A058250(k) for all k < m then m is a term.

MATHEMATICA

q[n_] := Product[Prime[i], {i, 1, n}]; fq[n_] := Product[Prime[i] - 1, {i, 1, n}];

a=0; Do[s=GCD[q[n], fq[n]]; If[s>a, a=s; Print[n]], {n, 1, 1000}]

CROSSREFS

Cf. A058250, A002110, A000010, A005867, A071350.