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

Author

N. J. A. Sloane, Nov 27 2007

Keywords

• nonn
• easy

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

• Tomás Oliveira e Silva, The px+1 problem
• Index entries for sequences related to 3x+1 (or Collatz) problem

Crossrefs

Cf. A133421, A133419, ...

Programs

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,88}] (* Harvey P. Dale, Dec 27 2007 *)

Extensions

More terms from Harvey P. Dale, Dec 27 2007

More terms from Sean A. Irvine, Mar 29 2010