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 A199637 Least odd number k such that in the Collatz sequence of k there are n even numbers. 2
 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 (list; graph; refs; listen; history; text; internal format)
 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

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Last modified June 25 04:09 EDT 2021. Contains 345452 sequences. (Running on oeis4.)