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A207675

Numbers such that not all divisors occur in their Collatz trajectories.

9, 15, 18, 21, 27, 30, 33, 35, 36, 39, 42, 45, 51, 54, 55, 57, 60, 63, 66, 69, 70, 72, 75, 77, 78, 81, 84, 85, 87, 90, 91, 93, 95, 96, 99, 102, 105, 108, 110, 111, 114, 115, 117, 119, 120, 121, 123, 125, 126, 129, 132, 133, 135, 138, 140, 141, 143, 144, 145

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OFFSET

1,1

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Eric Weisstein's World of Mathematics, Collatz Problem

Wikipedia, Collatz conjecture

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

EXAMPLE

3 is a divisor of 9, not occurring in A033479 - therefore 9 is a term.

MATHEMATICA

coll[n_]:=NestWhileList[If[EvenQ[#], #/2, 3#+1]&, n, #>1&]; Select[Range[145], Complement[Divisors[#], coll[#]]!={}&] (* Jayanta Basu, May 27 2013 *)