OFFSET
2,1
COMMENTS
What is the asymptotic behavior of the sequences defined by the recursive map x -> a(x)? Do these sequences increase without bound or do they enter a repeating cycle?
For example, the trajectory of 11 under the above map starts 11, 2047, 23, 8388607, 47, 140737488355327, 2351, s, 4703, t, ..., where s is a 708-digit number and t is a 1416-digit number. t has no prime factor less than 2^64 (cf. GIMPS link).
PROG
(PARI) a(n) = if(ispseudoprime(n), 2^n-1, factor(n)[1, 1])
CROSSREFS
KEYWORD
nonn
AUTHOR
Felix Fröhlich, May 30 2019
STATUS
approved