A221468 The Collatz (3x+1) iteration in A220145 converted to decimal.

1, 2, 133, 4, 33, 266, 67733, 8, 541865, 66, 16933, 532, 529, 135466, 135253, 16, 4233, 1083730, 1083717, 132, 129, 33866, 33813, 1064, 8669737, 1058, 2678946987458595510314019806849701, 270932, 270929, 270506, 83717093358081109697313118964053, 32, 69357897

Offset: 1

Author

T. D. Noe, Jan 17 2013

Keywords

• nonn
• base
• look

Comments

Sequence A005186 tells how many of these numbers are in [2^n, 2^(n+1)-1].

From Rémy Sigrist, Aug 19 2017: (Start)

a(2^n) = 2^n for any n >= 0.

A000120(a(n)) - 1 = A006667(n) for any n > 0.

A070939(a(n)) - 1 = A006577(n) for any n > 0.

All terms are Fibbinary numbers (A003714).

(End)

Links

• Rémy Sigrist, Table of n, a(n) for n = 1..10000
• Index entries for sequences related to 3x+1 (or Collatz) problem

Crossrefs

Cf. A000120, A003714, A005186, A006577, A006667, A070939, A220145.

Programs

Mathematica

Table[FromDigits[#, 2] &@ Boole@ OddQ@ Reverse@ NestWhileList[If[EvenQ@ #, #/2, 3 # + 1] &, n, # > 1 &], {n, 33}] (* Michael De Vlieger, Aug 19 2017 *)

PARI

a(n) = my (v=0, p=1); while (n>1, if (n%2, n = 3*n+1; v += p, n = n/2); p *= 2); return (p+v) \\ Rémy Sigrist, Aug 19 2017