A176868 Greatest odd number that requires n Collatz (3x+1) iterations to reach 1, or zero if there is no such number.

1, 0, 0, 0, 0, 5, 0, 21, 0, 85, 0, 341, 113, 1365, 453, 5461, 1813, 21845, 7281, 87381, 29125, 349525, 116501, 1398101, 466033, 5592405, 1864133, 22369621, 7456533, 89478485, 29826161, 357913941, 119304645, 1431655765, 477218581, 5726623061, 1908874353

Offset: 0

Author

T. D. Noe, Apr 27 2010

Keywords

• nonn

Comments

Both the 3x+1 steps and the halving steps are counted. a(n)=0 only for n = 1, 2, 3, 4, 6, 8, and 10.

Links

• T. D. Noe, Table of n, a(n) for n = 0..400

Crossrefs

Cf. A176866, A176867.

Programs

Mathematica

nn = 10; t1 = {0, 0, 5, 21, 85, 341, 1365}; Do[AppendTo[t1, 4 t1[[-1]] + 1], {3*nn}]; t2 = {1, 0, 0, 0, 0, 0, 113}; Do[AppendTo[t2, 4 t2[[-1]] + 1]; AppendTo[t2, 4 t2[[-1]] + 1]; AppendTo[t2, 4 t2[[-1]] + 29], {nn}]; t = Riffle[t2, t1] (* T. D. Noe, Feb 14 2013 *)