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 A062057 Numbers with 7 odd integers in their Collatz (or 3x+1) trajectory. 7
 9, 18, 19, 36, 37, 38, 72, 74, 76, 77, 81, 144, 148, 149, 152, 154, 162, 163, 288, 296, 298, 304, 308, 309, 321, 324, 325, 326, 331, 576, 592, 596, 597, 608, 616, 618, 625, 642, 643, 648, 650, 652, 653, 662, 663, 713, 715, 1152, 1184, 1192, 1194, 1216, 1232, 1236, 1237 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The Collatz (or 3x+1) function is f(x) = x/2 if x is even, 3x+1 if x is odd. The Collatz trajectory of n is obtained by applying f repeatedly to n until 1 is reached. A078719(a(n)) = 7; A006667(a(n)) = 6. REFERENCES J. Shallit and D. Wilson, The "3x+1" Problem and Finite Automata, Bulletin of the EATCS #46 (1992) pp. 182-185. LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..1000 J. Shallit and D. Wilson, The "3x+1" Problem and Finite Automata, Bulletin of the EATCS #46 (1992) pp. 182-185. Eric Weisstein's World of Mathematics, Collatz Problem Wikipedia, Collatz conjecture EXAMPLE The Collatz trajectory of 9 is (9, 28, 14, 7, 22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1), which contains 7 odd integers. MATHEMATICA Collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, n, # > 1 &]; countOdd[lst_] := Length[Select[lst, OddQ]]; Select[Range[1000], countOdd[Collatz[#]] == 7 &] (* T. D. Noe, Dec 03 2012 *) PROG (Haskell) import Data.List (elemIndices) a062057 n = a062057_list !! (n-1) a062057_list = map (+ 1) \$ elemIndices 7 a078719_list -- Reinhard Zumkeller, Oct 08 2011 CROSSREFS Cf. A062052-A062060. Sequence in context: A107977 A257226 A092457 * A254066 A015785 A316438 Adjacent sequences:  A062054 A062055 A062056 * A062058 A062059 A062060 KEYWORD nonn AUTHOR STATUS approved

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Last modified June 20 17:31 EDT 2021. Contains 345189 sequences. (Running on oeis4.)