OFFSET
1,1
COMMENTS
The Collatz iteration of primes of the form (10*4^k-1)/3 produces only one additional prime: 5. The Collatz iteration of primes of the form (13*4^k-1)/3 produces only two additional primes: 5 and 13. This sequence is probably infinite.
In a sense, these are the simplest Collatz iterations starting with a prime number. Except for the increases (3x+1) when an odd prime occurs, the sequence produced by starting with a(n) is decreasing. All the primes that occur in such a Collatz iteration are in this sequence. - T. D. Noe, Oct 05 2011
LINKS
Donovan Johnson and T. D. Noe, Table of n, a(n) for n = 1..10000 (Donovan Johnson to 203 terms)
Eric Weisstein's World of Mathematics, Collatz Problem
Wikipedia, Collatz conjecture
EXAMPLE
The Collatz iteration of 7 produces 7, 22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, and 1, which are either even, prime, or 1.
MATHEMATICA
Collatz[n_] := NestWhileList[If[EvenQ[ # ], #/2, 3#+1] &, n, #>1 &]; Reap[Do[p=Prime[n]; s=Most[Select[Collatz[p], OddQ]]; If[And@@PrimeQ[s], Sow[p]], {n, PrimePi[10^4]}]][[2, 1]]
oenQ[n_]:=AllTrue[DeleteCases[Most[NestWhileList[If[EvenQ[#], #/2, 3#+1]&, n, #>1&]], _?PrimeQ], EvenQ]; Select[Prime[Range[5000]], oenQ] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Dec 28 2014 *)
PROG
(Haskell)
a177000 n = a177000_list !! (n-1)
a177000_list = filter (all (\x -> even x || a010051' x == 1) .
(init . a070165_row)) a000040_list
-- Reinhard Zumkeller, Apr 03 2012
(PARI) is(n)=isprime(n) && (n<23 || is((3*n+1)>>valuation(3*n+1, 2))) \\ Charles R Greathouse IV, Jun 20 2013
CROSSREFS
KEYWORD
nonn,nice
AUTHOR
T. D. Noe, Apr 30 2010
STATUS
approved