gistfile1.txt

cf3 =
 Compile[
  {},
  Module[
   {n1, l, max = 0, maxN = 0},
   Do[
    n1 = n;
    l = 1;
    While[
     n1 != 1,
     n1 = If[EvenQ[n1], n1~Quotient~2, 3 n1 + 1];
     l++];
    If[l > max, max = l; maxN = n];,
    {n, 1, 10^4}];
   {max, maxN}]]

cf =
 Compile[
  {},
  Module[
   {n1, l, maxLength = 0, maxStart = 0},
   Do[
    n1 = n;
    l = 1;
    While[
     n1 != 1,
     n1 = If[EvenQ[n1], n1/2, 3 n1 + 1];
     l++];
    If[l > maxLength, maxLength = l; maxStart = n];,
    {n, 1, 10^4}];
   {maxLength, maxStart}]]