

A260144


Numbers k such that there exist two numbers a and b where k = a.b = sigma(a)*phi(b) ("." means concatenation).


2




OFFSET

1,1


COMMENTS

The sequence is infinite because, for m>0, 14049280*10^m = sigma(1404) * phi(9280*10^m).
a(7) > 10^10.


LINKS

Table of n, a(n) for n=1..6.


EXAMPLE

1568 is in the sequence because 1568 = sigma(156) * phi(8).


CROSSREFS

Cf. A000010, A000203, A159000, A253824.
Sequence in context: A232036 A035765 A107561 * A221105 A236261 A252073
Adjacent sequences: A260141 A260142 A260143 * A260145 A260146 A260147


KEYWORD

nonn,base,more


AUTHOR

Paolo P. Lava and Giovanni Resta, Jul 17 2015


STATUS

approved



