A199818 Odd numbers producing 20 even numbers in the Collatz iteration.

43, 131, 133, 397, 405, 433, 435, 441, 475, 1237, 1251, 1285, 1301, 1313, 1325, 1339, 1425, 1427, 1431, 1433, 3861, 3925, 3939, 3941, 3981, 4017, 4019, 4043, 4277, 4293, 4297, 4301, 11605, 11829, 12053, 12131, 12133, 12853, 12885, 12893, 12913, 12931, 36181

Offset: 1

Author

Vincenzo Librandi, Nov 12 2011

Keywords

• nonn

Comments

For n <10000000, more terms: 36405, 38677, 38741, 38797, 38833, 38835, 116053, 116501, 349525.

See row 20 of A199636. There are A131450(20) = 52 terms. - T. D. Noe, Nov 18 2011

Crossrefs

Cf. A199636.

Programs

Mathematica

Collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, n, # > 1 &]; t = {}; Do[If[Length[Select[Collatz[n], EvenQ]] == 20, AppendTo[t, n]], {n, 1, 100000, 2}]; t