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

0,2

Comments

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

Links

Table of n, a(n) for n=0..4.

Example

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.

Prog

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

Crossrefs

Cf. A000010, A000203, A055681.

Sequence in context: A280734 A048830 A038081 * A027737 A063970 A309864

Adjacent sequences: A291255 A291256 A291257 * A291259 A291260 A291261

Keyword

nonn,more

Author

Altug Alkan, Aug 21 2017

Status

approved