Numbers n such that n is in the 3x+1 (Colatz) trajectory of n-1.
4, 8, 10, 16, 20, 26, 34, 40, 52, 92, 122, 160, 167, 184, 244, 251, 334, 377, 412, 433, 488, 502, 650, 668, 866, 890, 976, 1154, 1186, 1300, 1336, 1732, 1780, 2308, 3644, 4858, 7288
1
No other terms less than 10^9.
T. D. Noe, Plot of 37 terms
(Mma) Collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, n, # > 1 &]; Select[Range[10000], MemberQ[Collatz[#-1], #] &]
Cf. A070993, A276200, S000963.
nonn,more
T. D. Noe, Jan 27 2017