A199637 Least odd number k such that in the Collatz sequence of k there are n even numbers.

5, 3, 21, 13, 85, 17, 11, 7, 15, 9, 19, 37, 25, 49, 33, 65, 43, 87, 57, 39, 79, 153, 105, 203, 135, 271, 185, 123, 247, 169, 329, 219, 159, 295, 569, 379, 283, 505, 377, 251, 167, 111, 223, 445, 297, 593, 395, 263, 175, 351, 233, 155, 103, 207, 137, 91, 183

Offset: 4

Author

T. D. Noe, Nov 14 2011

Keywords

• nonn

Comments

Previous name was: First number in row n of triangle A199636.

Links

• Robert G. Wilson v, Table of n, a(n) for n = 4..573 (first 500 terms from T. D. Noe)

Crossrefs

Cf. A199636.

Programs

Mathematica

Collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, n, # > 1 &]; nn = 100; t = Table[0, {nn}]; cnt = 3; n = 1; While[cnt < nn, n = n + 2; len = Length[Select[Collatz[n], EvenQ]]; If[len <= nn && t[[len]] == 0, t[[len]] = n; cnt++]]; t
f = Compile[{{n, Real}}, Block[{c = 0, k = n}, While[k > 1, c++; If[OddQ@ Round@ k, k = (3k + 1)/2, k /= 2]]; c]]; k = 1; t[] := 0; While[k < 2101, If[t@ f@ k == 0, t@ f@ k = k;]; k += 2]; t@# & /@ Range@ 100 (* Robert G. Wilson v, Mar 06 2018 *)

Extensions

New name from Robert G. Wilson v, Mar 06 2018