[seqfan] Iterating sigma - 1

[franktaw at netscape.net]

Consider http://www.research.att.com/~njas/sequences/A039654 - Prime 
reached by iterating f(x) = sigma(x)-1 on n.

It isn't obvious that this iteration always reaches a prime, although 
it seems nearly certain that it does. Should we add something like ", 
or 0 if no prime is ever reached", with a comment that apparently the 
sequence always does reach a prime? (Or can someone prove that a prime 
is always reached?)

One might, in this case, also add a(1) = 0 (suitably modifying the 
comment).

Franklin T. Adams-Watters