A207675 Numbers such that not all divisors occur in their Collatz trajectories.

9, 15, 18, 21, 27, 30, 33, 35, 36, 39, 42, 45, 51, 54, 55, 57, 60, 63, 66, 69, 70, 72, 75, 77, 78, 81, 84, 85, 87, 90, 91, 93, 95, 96, 99, 102, 105, 108, 110, 111, 114, 115, 117, 119, 120, 121, 123, 125, 126, 129, 132, 133, 135, 138, 140, 141, 143, 144, 145

Offset

1,1

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Eric Weisstein's World of Mathematics, Collatz Problem

Wikipedia, Collatz conjecture

Index entries for sequences related to 3x+1 (or Collatz) problem

Example

3 is a divisor of 9, not occurring in A033479 - therefore 9 is a term.

Mathematica

coll[n_]:=NestWhileList[If[EvenQ[#], #/2, 3#+1]&, n, #>1&]; Select[Range[145], Complement[Divisors[#], coll[#]]!={}&] (* Jayanta Basu, May 27 2013 *)

Prog

(Haskell)
import Data.List (intersect)
a207675 n = a207675_list !! (n-1)
a207675_list = filter
   (\x -> a027750_row x `intersect` a070165_row x /= a027750_row x) [1..]

Crossrefs

Cf. A027750, A070165, A006370, A207674 (complement).

Sequence in context: A093642 A364566 A177733 * A118236 A230306 A070876

Adjacent sequences: A207672 A207673 A207674 * A207676 A207677 A207678

Keyword

nonn

Author

Reinhard Zumkeller, Feb 20 2012

Status

approved