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 A198584 Odd numbers producing 3 odd numbers in the Collatz (3x+1) iteration. 14
 3, 13, 53, 113, 213, 227, 453, 853, 909, 1813, 3413, 3637, 7253, 7281, 13653, 14549, 14563, 29013, 29125, 54613, 58197, 58253, 116053, 116501, 218453, 232789, 233013, 464213, 466005, 466033, 873813, 931157, 932053, 932067, 1856853, 1864021, 1864133 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS One of the odd numbers is always 1. So besides a(n), there is one other odd number, A198585(n), which is a term in A002450. Sequences A228871 and A228872 show that there are two sequences here: the odd numbers in order and out of order. - T. D. Noe, Sep 12 2013 LINKS T. D. Noe, Table of n, a(n) for n = 1..1009 EXAMPLE The Collatz iteration of 113 is 113, 340, 170, 85, 256, 128, 64, 32, 16, 8, 4, 2, 1, which shows that 113, 85, and 1 are the three odd terms. MATHEMATICA Collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, n, # > 1 &]; t = {}; Do[If[Length[Select[Collatz[n], OddQ]] == 3, AppendTo[t, n]], {n, 1, 10000, 2}]; t PROG (Python) # get n-th term in sequence def isqrt(n):   i=0   while(i*i<=n):     i+=1   return i-1 for n in range (200):   s = isqrt(3*n)//3   a = s*3   b = (a*a)//3   c = n-b   d = 4*(n*3+a+(c4*s+1)+(c>5*s+1))+5   e = isqrt(d)   f = e-1-( (d-e*e) >> 1 )   r = ((((8<

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Last modified May 8 15:40 EDT 2021. Contains 343666 sequences. (Running on oeis4.)