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A221475
Odd numbers having no odd primes in their Collatz (3x+1) trajectory.
3
1, 21, 85, 341, 453, 909, 1365, 1813, 5461, 7281, 9669, 21845, 29013, 29125, 38835, 45839, 54327, 58197, 58253, 68759, 77667, 81491, 87381, 103139, 116053, 116501, 122237, 154709, 154737, 155341, 183357, 232789, 233013, 257551, 275037, 310385, 310669, 325965
OFFSET
1,2
COMMENTS
Sequence A196871 contains these terms and even numbers that are 2^k times terms in this sequence.
MATHEMATICA
Collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, n, # > 1 &]; t = {1}; n = 1; While[Length[t] < 50, n = n + 2; If[Union[Drop[PrimeQ[Collatz[n]], -2]] == {False}, AppendTo[t, n]]]; t
CROSSREFS
Cf. A196871.
Sequence in context: A044589 A374527 A116972 * A277356 A041858 A217549
KEYWORD
nonn
AUTHOR
T. D. Noe, Feb 14 2013
STATUS
approved