A133422 Number of steps to reach 1 under repeated applications of the "7x+1" map of A133421, or -1 if 1 is never reached.

0, 1, 1, 2, 1, 2, 4, 3, 2, 2, 12, 3, 9, 5, 2, 4, 6, 3, 21, 3, 5, 13, 6, 4, 2, 10, 3, 6, 10, 3, 47, 5, 13, 7, 5, 4, 13, 22, 10, 4, 8, 6, 46, 14, 3, 7, 16, 5, 50, 3, 7, 11, 51, 4, 13, 7, 22, 11, 10, 4, 9, 48, 6, 6, 10, 14, 19, 8, 7, 6, 17, 5, 10, 14, 3, 23, 7, 11, 17, 5, 4, 9, 14, 7, 7, 47, 11, 15

Offset

1,4

Comments

The 7x+1 map sends x to x/2 if x is even, x/3 if x is divisible by 3, x/5 if x is divisible by 5, otherwise 7x+1.

Links

Table of n, a(n) for n=1..88.

Tomás Oliveira e Silva, The px+1 problem

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

Mathematica

nxt[x_]:= Which[Mod[x, 2]==0, x/2, Mod[x, 3]==0, x/3, Mod[x, 5]==0, x/5, True, 7x+1]; Table[First[First[Position[NestList[nxt, i, 100], 1]]]-1, {i, 50}] - Harvey P. Dale, Dec 27 2007

Crossrefs

Cf. A133421, A133419, ...

Sequence in context: A101897 A208058 A078142 * A331136 A099312 A117505

Adjacent sequences: A133419 A133420 A133421 * A133423 A133424 A133425

Keyword

nonn,easy

Author

N. J. A. Sloane, Nov 27 2007

Extensions

More terms from Harvey P. Dale, Dec 27 2007

More terms from Sean A. Irvine, Mar 29 2010

Status

approved