A228872 Odd numbers producing 3 decreasing odd numbers in the Collatz (3x+1) iteration.

13, 53, 113, 213, 453, 853, 909, 1813, 3413, 3637, 7253, 7281, 13653, 14549, 29013, 29125, 54613, 58197, 58253, 116053, 116501, 218453, 232789, 233013, 464213, 466005, 466033, 873813, 931157, 932053, 1856853, 1864021, 1864133, 3495253, 3724629, 3728213

Offset: 1

Author

T. D. Noe, Sep 12 2013

Keywords

• nonn

Comments

Sequence A198584 gives the first term of the Collatz sequence having exactly 3 odd numbers. This sequence is the subset of A198584 for which the second odd number is smaller than the first.

Examples

			The number 13 has the Collatz iteration {13, 40, 20, 10, 5, 16, 8, 4, 2, 1}, which has three odd numbers in decreasing order {13, 5, 1}.
		

Crossrefs

Cf. A198584 (Collatz iterations having 3 odd numbers).

Cf. A228871 (Collatz iterations producing 3 out-of-order odd numbers).

Programs

Mathematica

donQ[n_]:=Module[{od=Differences[Select[NestWhileList[If[EvenQ[#],#/2,3#+1]&,n,#>1&], OddQ]]}, Length[ od] ==2&&Max[od]<0]; Select[Range[1,373*10^4,2],donQ] (* Harvey P. Dale, Sep 23 2019 *)