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 A213678 Number of terms k such that difference between halving and tripling steps in Collatz (3x+1) trajectory of k is n. 2
 1, 1, 1, 3, 3, 5, 8, 14, 20, 29, 40, 59, 87, 130, 196, 294, 439, 658, 985, 1459, 2203, 3328, 5001, 7482, 11205, 16805, 25220, 37850, 56713, 85108, 127728, 191635 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 LINKS Table of n, a(n) for n=0..31. EXAMPLE a(5) = 5 since there are only five numbers 12, 13, 20, 21, 32 such that difference between number of halving and tripling steps is 5. MATHEMATICA Collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, n, # > 1 &]; nn = 15; t = Table[0, {nn}]; Do[c = Collatz[n]; e = Select[c, EvenQ]; diff = 2*Length[e] - Length[c]; If[diff < nn - 1, t[[diff + 2]]++], {n, 2^(nn - 1)}]; t (* T. D. Noe, Mar 04 2013 *) CROSSREFS Cf. A220071, A222599 (lists of numbers). Sequence in context: A200737 A200741 A271970 * A293676 A303714 A098353 Adjacent sequences: A213675 A213676 A213677 * A213679 A213680 A213681 KEYWORD nonn AUTHOR Jayanta Basu, Mar 04 2013 EXTENSIONS Corrected and extended by T. D. Noe, Mar 06 2013 STATUS approved

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Last modified June 10 05:41 EDT 2023. Contains 363195 sequences. (Running on oeis4.)