%I #11 Apr 07 2015 11:11:16

%S 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,

%T 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,

%U 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

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

%C 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.

%H Tomás Oliveira e Silva, <a href="http://sweet.ua.pt/tos/3x+1.html">The px+1 problem</a>

%H <a href="/index/3#3x1">Index entries for sequences related to 3x+1 (or Collatz) problem</a>

%t 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

%Y Cf. A133421, A133419, ...

%K nonn,easy

%O 1,4

%A _N. J. A. Sloane_, Nov 27 2007

%E More terms from _Harvey P. Dale_, Dec 27 2007

%E More terms from _Sean A. Irvine_, Mar 29 2010