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A308712 a(0) = 0 and a(1) = 1; for n > 0, a(n) = a(n-1)/2 if that number is an integer and not already in the sequence, otherwise a(n) = 3*a(n-1) + remainder of a(n-1)/2.  (A variant of the Collatz sequence). 0
0, 1, 4, 2, 6, 3, 10, 5, 16, 8, 24, 12, 36, 18, 9, 28, 14, 7, 22, 11, 34, 17, 52, 26, 13, 40, 20, 60, 30, 15, 46, 23, 70, 35, 106, 53, 160, 80, 240, 120, 360, 180, 90, 45, 136, 68, 204, 102, 51, 154, 77, 232, 116, 58, 29, 88, 44, 132, 66, 33, 100, 50, 25, 76, 38, 19, 58 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Similar to A128333 and related to the 3x+1 (Collatz) sequence. Hits all positive integers?

LINKS

Table of n, a(n) for n=0..66.

EXAMPLE

a(1)=1 => a(2)=3*1+1=4 because a(1) is odd => a(3)=4/2=2 because a(2) is even => a(4)=3*2+0=6 because a(3) is even but a(3)/2 is already in the sequence.

MATHEMATICA

a[0] = 0; a[1] = 1; a[n_] := a[n] = With[{b = a[n-1]}, If[EvenQ[b] && FreeQ[Array[a, n, 0], b/2], b/2, 3 b + Mod[b, 2]]];

Table[a[n], {n, 0, 100}] (* Jean-François Alcover, Jun 20 2019 *)

CROSSREFS

Cf. A126038, A005132, A128333.

Sequence in context: A257908 A097467 A169839 * A275845 A281978 A325887

Adjacent sequences:  A308709 A308710 A308711 * A308713 A308714 A308715

KEYWORD

easy,nonn

AUTHOR

Alexis Monnerot-Dumaine, Jun 19 2019

STATUS

approved

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Last modified March 31 18:53 EDT 2020. Contains 333151 sequences. (Running on oeis4.)