

A291258


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


0




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 A130769
Adjacent sequences: A291255 A291256 A291257 * A291259 A291260 A291261


KEYWORD

nonn,more


AUTHOR

Altug Alkan, Aug 21 2017


STATUS

approved



