A067385 a(n) is smallest x such that sigma(phi(x))/sigma(x) = n.

1, 13, 181, 121679, 1033474069

Offset: 1

Author

Dean Hickerson, Jan 20 2002

Keywords

• nonn
• more

Comments

A023199(6) < a(6) <= 1794819234390989. - Donovan Johnson, Oct 24 2011

Crossrefs

Cf. A023199, A033631, A066831, A067382, A067383, A067384, A197952.

Programs

Mathematica

a[ n_ ] := For[ x=1, True, x++, If[ DivisorSigma[ 1, EulerPhi[ x ] ]/DivisorSigma[ 1, x ]==n, Return[ x ] ] ]

Extensions

a(5) from Vim Wenders, Mar 11 2007