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A238192 In the Collatz (3x+1) iteration of n, the last odd number before 1, or 0 if there is no such number. 3
0, 0, 5, 0, 5, 5, 5, 0, 5, 5, 5, 5, 5, 5, 5, 0, 5, 5, 5, 5, 21, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 0, 5, 5, 5, 5, 5, 5, 5, 5, 5, 21, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 0, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 85, 5, 5, 5, 5, 5, 5, 5, 5, 21, 85, 5 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Another version of A237660. The only terms appearing here are 0, 5, 21, 85, ..., which is A002450 without 1.

LINKS

T. D. Noe, Table of n, a(n) for n = 1..10000

MATHEMATICA

Collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, n, # > 1 &]; Table[c = Collatz[n]; co = Select[c, OddQ]; If[Length[co] == 1, 0, co[[-2]]], {n, 100}]

CROSSREFS

Cf. A002450 ((4^n-1)/3), A070165 (Collatz trajectories).

Sequence in context: A261839 A091672 A144702 * A156716 A055510 A200397

Adjacent sequences:  A238189 A238190 A238191 * A238193 A238194 A238195

KEYWORD

nonn

AUTHOR

T. D. Noe, Feb 21 2014

STATUS

approved

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Last modified June 19 23:18 EDT 2021. Contains 345153 sequences. (Running on oeis4.)