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

1, 13, 181, 121679, 1033474069

Offset

1,2

Comments

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

Links

Table of n, a(n) for n=1..5.

Mathematica

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

Crossrefs

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

Sequence in context: A239902 A020544 A009015 * A097260 A178303 A158548

Adjacent sequences: A067382 A067383 A067384 * A067386 A067387 A067388

Keyword

nonn,more

Author

Dean Hickerson, Jan 20 2002

Extensions

a(5) from Vim Wenders, Mar 11 2007

Status

approved