OFFSET
1,1
COMMENTS
EXAMPLE
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}.
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 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
T. D. Noe, Sep 12 2013
STATUS
approved