A198590 Odd numbers producing 7 odd numbers in the Collatz iteration.

9, 19, 37, 77, 81, 149, 163, 309, 321, 325, 331, 597, 625, 643, 653, 663, 713, 715, 1237, 1251, 1285, 1301, 1313, 1325, 1339, 1425, 1427, 1431, 1433, 2389, 2501, 2573, 2577, 2613, 2625, 2627, 2653, 2679, 2695, 2851, 2853, 2861, 2865, 2867, 4949, 5005, 5141

Offset: 1

Author

T. D. Noe, Oct 31 2011

Keywords

• nonn

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1046

Crossrefs

Cf. A198584.

Programs

Mathematica

Collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, n, # > 1 &]; t = {}; Do[If[Length[Select[Collatz[n], OddQ]] == 7, AppendTo[t, n]], {n, 1, 10000, 2}]; t
col7Q[n_]:=Length[Select[NestWhileList[If[EvenQ[#],#/2,3#+1]&,n,#>1&],OddQ]]==7; Select[ Range[1,5201,2],col7Q] (* Harvey P. Dale, Sep 25 2023 *)