A291258 a(n) is the smallest number k such that sigma(k) - phi(k) = n*k, or 0 if no such k exists.

1, 2, 12, 75960, 17156160

Offset: 0

Author

Altug Alkan, Aug 21 2017

Keywords

• nonn
• more

Comments

a(5) and following terms > 10^13, if they exist. - Giovanni Resta, Aug 21 2017

Examples

			a(2) = 12 because sigma(12) = 28, phi(12) = 4; sigma(12) - phi(12) = 2*12 and 12 is the smallest number with this property.
		

Crossrefs

Cf. A000010, A000203, A055681.

Programs

PARI

a(n) = {my(k=1); while (sigma(k)-eulerphi(k)!=n*k, k++); k; }