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A139391
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Next odd term in Collatz trajectory with starting value n.
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25
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1, 1, 5, 1, 1, 3, 11, 1, 7, 5, 17, 3, 5, 7, 23, 1, 13, 9, 29, 5, 1, 11, 35, 3, 19, 13, 41, 7, 11, 15, 47, 1, 25, 17, 53, 9, 7, 19, 59, 5, 31, 21, 65, 11, 17, 23, 71, 3, 37, 25, 77, 13, 5, 27, 83, 7, 43, 29, 89, 15, 23, 31, 95, 1, 49, 33, 101, 17, 13, 35, 107, 9, 55, 37, 113, 19, 29
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OFFSET
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1,3
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LINKS
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FORMULA
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MATHEMATICA
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a[n_]:=Select[NestWhileList[If[EvenQ[#], #/2, 3#+1] &, n, #>1 &], OddQ]; Prepend[Table[If[EvenQ[n], a[n][[1]], a[n][[2]]], {n, 2, 77}], 1] (* Jayanta Basu, May 27 2013 *)
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PROG
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(Python) # first formula
def A006370(n): return 3*n+1 if n%2 else n//2
def a(n): return x if (x := A006370(n))%2 else a(x)
(Python) # fourth formula, uses A006370 above
while n%2 == 0: n //= 2
return n
(PARI) a(n) = my(x = if(n%2, 3*n+1, n/2)); x/2^valuation(x, 2); \\ Michel Marcus, Feb 27 2022
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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