A237660 -id:A237660 - cp's OEIS frontend

A237661 Indices of records in A237660.

3, 42, 75, 151, 2730, 7281, 14563, 174762, 184111, 932067, 11184810, 13256071, 26512143, 715827882, 1908874353

Offset: 1

Kival Ngaokrajang, Feb 11 2014

Charles R Greathouse IV, C code to find initial terms

C
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See Greathouse link
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With[{s = Table[If[AllTrue[#, EvenQ], 0, SelectFirst[Reverse@ #, OddQ]] &@ Most@ Rest@ NestWhileList[If[EvenQ@ #, #/2, (3 # + 1)/2] &, n, # > 1 &], {n, 2, 10^5}] }, 1 + Values[#][[All, 1]] &@ Rest@ KeySort@ PositionIndex@ s] (* Michael De Vlieger, Aug 14 2017 *)

A237660(n)=my(k); if(n%2,n=3*n+1); n>>=valuation(n,2); if(n==1,return(0)); k=n; while(1, n+=(n+1)>>1; n>>=valuation(n,2); if(n==1, return(k), k=n))
r=0; for(n=1,1e8, t=A237660(n); if(t>r, r=t; print1(n", "))) \\ Charles R Greathouse IV, Aug 14 2017

a(11)-a(15) from Charles R Greathouse IV, Aug 14 2017

A238192 In the Collatz (3x+1) iteration of n, the last odd number before 1, or 0 if there is no such number.

Original entry on oeis.org

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

Offset: 1

T. D. Noe, Feb 21 2014

nonn

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

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

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

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}]

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A237661 Indices of records in A237660.

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