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A322521
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If A319303(k) = n for some k, then a(n) = k, else a(n) = -1.
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2
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0, 1, 12, 2, 6, 16, 198, 3, 454, 8, 102, 20, 22, 262, 378, 4, 54, 582, 742, 10, 11, 134, 186, 24, 1766, 30, 918403141209018, 326, 358, 506, 214715699432378, 5, 3814, 70, 90, 710, 774, 998, 51174, 14, 496190676143034, 15, 6918, 166, 182, 250, 109162583165882
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OFFSET
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1,3
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COMMENTS
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If the Collatz conjecture is true, then this sequence contains every nonnegative integers.
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LINKS
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EXAMPLE
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A319303(18) = 80, hence a(80) = 18.
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MATHEMATICA
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a[n0_] := Module[{n=n0, v=0}, While[n>1, t = If[OddQ[n], 3n+1, n/2]; If[t>4 && Mod[t+2, 6] == 0, v *= 2; v += Mod[n, 2]]; n = t; v++]; v]
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PROG
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(PARI) a(n) = my (v=0); while (n>1, my (t=if (n%2, 3*n+1, n/2)); if (t>4 && (t+2)%6==0, v*=2; v+=n%2); n=t; v++); v
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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