OFFSET
1,1
COMMENTS
a(24) > 10^9.
EXAMPLE
a(3) = 294 because sigma(sigma(sigma(2*3*7^2))) = 2^5*3*7^2 and 2*3*7^2 = 294 is the least number with this property.
MATHEMATICA
f[n_] := Block[{k = 2}, While[ Transpose[ FactorInteger[ Nest[ DivisorSigma[1, #] &, k, n]]][[1]] != Transpose[ FactorInteger[ k]][[1]], k += 2]; k]; (* Robert G. Wilson v, Aug 03 2017 *)
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Altug Alkan, Aug 03 2017
EXTENSIONS
a(10)-a(23) from Giovanni Resta, Aug 03 2017
STATUS
approved