OFFSET
1,1
COMMENTS
No further terms up to 2*10^9. It is conjectured that this is the full list of starting values of Collatz trajectories reaching k-1 or k+1, and that the number of steps until this happens is one of the 8 terms of A355240.
There are no further terms up to 31100000000. - Dmitry Kamenetsky, Oct 17 2022
LINKS
PROG
(Python)
def f(x): return 3*x+1 if x%2 else x//2
def ok(n):
if n < 5: return False
ni, targets = n, {1, n-1, n+1}
while ni not in targets: ni = f(ni)
return ni in {n-1, n+1}
print([k for k in range(10**4) if ok(k)]) # Michael S. Branicky, Jul 04 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Hugo Pfoertner, Jul 04 2022
STATUS
approved