OFFSET
1,2
COMMENTS
Only members of A028982 are candidates. - Robert G. Wilson v, Aug 27 2004
Question: iterating sigma()=A000203, how many iterates can be odd numbers?
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..500
EXAMPLE
n = 1910^2, sigma(n) = 2821^2, sigma(sigma(n)) = 10357983.
MATHEMATICA
t = Sort[ Flatten[ Table[{n^2, 2n^2}, {n, 36650}]]]; a = {}; Do[ If[ OddQ[ DivisorSigma[1, DivisorSigma[1, t[[n]] ]]], AppendTo[a, t[[n]] ]], {n, 2*10^6}]; a (* Robert G. Wilson v, Aug 27 2004 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Aug 24 2004
EXTENSIONS
Edited and extended by Robert G. Wilson v, Aug 27 2004
STATUS
approved