OFFSET
1,1
LINKS
Michael De Vlieger, Table of n, a(n) for n = 1..10000
EXAMPLE
All odd and certain even integers belong here.
MATHEMATICA
Flatten@ Table[Function[s, If[Length@ # > 0, First@ #, #] &@ Keys@ KeySelect[s, Length@ Lookup[s, #] == 1 &]]@ PositionIndex@ NestList[EulerPhi@ DivisorSigma[1, #] &, n, 10^2], {n, 71}] (* Michael De Vlieger, Jul 24 2017 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Jul 16 2004
STATUS
approved