A260144 Numbers k such that there exist two numbers a and b where k = a.b = sigma(a)*phi(b) ("." means concatenation).

1568, 14049280, 140492800, 368089904, 506300928, 1404928000, 14049280000, 124856008704, 140492800000, 1404928000000, 14049280000000, 15860872839168, 140492800000000

Offset

1,1

Comments

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

Links

Table of n, a(n) for n=1..13.

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

Extensions

a(7)-a(13) from Max Alekseyev, Sep 25 2025

Status

approved