A060565 Follow trajectory of 2n+1 in the '3x+1' problem until a lower number is reached; A060445 gives number of steps for this to happen. Sequence gives the first lower number that is reached.

2, 4, 5, 7, 10, 10, 10, 13, 11, 16, 20, 19, 23, 22, 23, 25, 20, 28, 38, 31, 37, 34, 46, 37, 29, 40, 47, 43, 38, 46, 61, 49, 38, 52, 61, 55, 64, 58, 76, 61, 47, 64, 74, 67, 61, 70, 91, 73, 56, 76, 61, 79, 91, 82, 61, 85, 65, 88, 101, 91, 118, 94, 77, 97, 74, 100, 86, 103

Offset

1,1

Links

Alois P. Heinz, Table of n, a(n) for n = 1..20000

Index entries for sequences related to 3x+1 (or Collatz) problem

Maple

b:= proc(n, t) option remember; `if`(n<t, n,
      b(`if`(n::even, n/2, 3*n+1), t))
    end:
a:= n-> b((2*n+1)$2):
seq(a(n), n=1..80);  # Alois P. Heinz, Jan 22 2022

Mathematica

b[n_, t_] := b[n, t] = If[n<t, n, b[If[EvenQ[n], n/2, 3n+1], t]];
a[n_] := b[2n+1, 2n+1];
Table[a[n], {n, 1, 80}] (* Jean-François Alcover, Apr 25 2022, after Alois P. Heinz *)

Prog

(PARI) a(n) = my(N=2*n+1, m=N); while(m >= N, m = if (m%2, 3*m+1, m/2)); m; \\ Michel Marcus, Jan 22 2022

Crossrefs

Cf. A060445.

Sequence in context: A078404 A056908 A296344 * A231014 A231009 A133254

Adjacent sequences: A060562 A060563 A060564 * A060566 A060567 A060568

Keyword

nonn,easy

Author

N. J. A. Sloane, Apr 12 2001

Extensions

More terms from Larry Reeves (larryr(AT)acm.org), Apr 13 2001

Status

approved