A216793 Numbers n such that gcd(sigma(n), n) > gcd(sigma(m), m) for all m < n.

1, 6, 24, 28, 120, 496, 672, 4320, 4680, 8128, 26208, 30240, 32760, 174592, 199584, 293760, 435708, 523776, 2142720, 2178540, 8910720, 17428320, 20427264, 23569920, 33550336, 45532800, 91963648, 142990848, 459818240, 1379454720, 1476304896, 6039429120

Offset: 1

Author

Michel Marcus, Sep 16 2012

Keywords

• nonn

Comments

a(30) > 10^9.

Examples

			a(2) = 6 because gcd(sigma(1), 1) = 1, gcd(sigma(2), 2) = 1, gcd(sigma(3), 3) = 1, gcd(sigma(4), 4) = 1, gcd(sigma(5), 5) = 1, and for n = 6, we have gcd(sigma(6), 6) = 6, which is greater than the five preceding.
		

Crossrefs

Cf. A009194.

Programs

PARI

mgcdab(n) = { m = 0; for (i=1, n, g = gcd(sigma(i), i); if (g > m, m = g; print1(i, ", ");););}

Extensions

a(30)-a(32) from Donovan Johnson, Sep 17 2012