OFFSET
1,1
COMMENTS
Question: does this sequence reach a cycle or does it increase without bound?
No cycle occurs in the first 324000 terms.
LINKS
Robert Israel, Table of n, a(n) for n = 1..6630
dxdy forum, post (in Russian).
Carlos Rivera, Puzzle 949. Another Collatz-like sequence
MATHEMATICA
Nest[Append[#, If[PrimeQ@ #[[-1]], #[[-1]]^2 + 9, Floor[#[[-1]]/2] ]] &, {2}, 25] (* Michael De Vlieger, Apr 21 2019 *)
PROG
(PARI) terms(n) = my(x=2, i=0); while(i < n, print1(x, ", "); i++; if(ispseudoprime(x), x=x^2+9, x=floor(x/2)))
/* Print initial 30 terms as follows: */
terms(30) \\ Felix Fröhlich, Apr 20 2019
CROSSREFS
KEYWORD
nonn,look
AUTHOR
Dmitry Kamenetsky, Apr 20 2019
STATUS
approved