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

4,1

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)

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 *)

Crossrefs

Cf. A199636.

Sequence in context: A084183 A099730 A072800 * A199636 A324038 A221473

Adjacent sequences: A199634 A199635 A199636 * A199638 A199639 A199640

Keyword

nonn

Author

T. D. Noe, Nov 14 2011

Extensions

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

Status

approved