A346591 Composite numbers k such that A006577(k) sets a new record.

4, 6, 9, 18, 25, 27, 54, 108, 129, 171, 231, 327, 649, 703, 871, 1161, 2223, 2463, 2919, 3711, 6171, 10971, 13255, 17647, 23529, 26623, 34239, 35655, 52527, 77031, 106239, 142587, 156159, 216367, 230631, 410011, 511935, 626331, 837799, 1117065, 1501353, 1723519

Offset

1,1

Links

Table of n, a(n) for n=1..42.

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

Mathematica

s[n_]:=s[n]=(i=0; r=n; While[r!=1, i++; If[EvenQ@r, r=r/2, r=r*3+1]]; i);
lst={}; max=1; Do[If[!PrimeQ@k, t=s[k]; If[t>max, AppendTo[lst, k]; max=t]], {k, 10^4}]; lst (* Giorgos Kalogeropoulos, Jul 28 2021 *)

Prog

(PARI) a6577(n0)={my(n=n0, k=0); while(n>1, k++; n=if(n%2, 3*n+1, n/2)); k};
a346591(limit)={msteps=0; forcomposite(c=4, limit, my(m=a6577(c)); if(m>msteps, print1(c, ", "); msteps=m))};
a346591(2000000)

Crossrefs

Cf. A006577, A346592, A346593.

A006877 is the union of A244638 and this sequence.

Sequence in context: A056016 A231997 A220144 * A152002 A171127 A098485

Adjacent sequences: A346588 A346589 A346590 * A346592 A346593 A346594

Keyword

nonn

Author

Hugo Pfoertner, Jul 28 2021

Status

approved