A182078 Odd numbers n such that the reduced Collatz map n -> (3n+1)/2^k gives a trajectory of decreasing odd numbers.

5, 13, 17, 21, 45, 53, 69, 85, 113, 141, 181, 213, 241, 277, 301, 321, 341, 369, 401, 453, 565, 725, 753, 853, 909, 965, 1069, 1109, 1137, 1205, 1285, 1365, 1425, 1477, 1605, 1713, 1813, 1933, 1969, 2261, 2417, 2573, 2577, 2625, 2901, 2957, 3013, 3213, 3413

Offset: 1

Author

Michel Lagneau, Apr 10 2012

Keywords

• nonn

Examples

			45 is in the sequence because 45 generates the trajectory of odd numbers : 45 -> 17 -> -> 13 -> 5 -> 1.
		

Links

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

Crossrefs

Cf. A006666, A075677 (reduced Collatz map), A256598 (trajectory).

Programs

Maple

for n from 3 by 2 to 5000 do:i:=0:x:=n:n0:=n: u0:=0:for it from 1 to 1000 while(n0<>1 and u0=0) do: for a from 1 to 100 while(x mod 2 = 0 ) do: i:=i+1:x:=x/2: od:if x > n0 then u0:=1:else i:=i+1:n0:=x :x:=3*n0+1: fi:od: if u0=0 then printf(`%d, `,n):else fi:od: