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A347669
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Indices of first occurrences of n in A347409.
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2
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1, 2, 4, 8, 3, 15, 21, 128, 75, 512, 151, 2048, 1365, 8192, 5461, 7407, 14563, 131072, 87381, 524288, 184111, 2097152, 932067, 6213783, 5592405, 33554432, 13256071, 134217728, 26512143, 530242875, 357913941, 1899273247, 1431655765, 8589934592, 3817748707, 34359738368
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OFFSET
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0,2
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LINKS
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EXAMPLE
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a(5) = 15 because 5 occurs for the first time at position 15 in A347409.
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MATHEMATICA
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A347409[n_]:=A347409[n]=(c=n; sm=0; While[c>1, If[OddQ[c], c=3c+1, If[(s=IntegerExponent[c, 2])>sm, sm=s]; c/=2^s]]; sm)
nterms=20; Table[i=0; While[A347409[++i]!=n]; i, {n, 0, nterms-1}]
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PROG
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(PARI) f(n) = {my(nb=0); while (n != 1, if (n % 2, n=3*n+1, my(x = valuation(n, 2)); n /= 2^x; nb = max(nb, x)); ); nb; } \\ A347409
a(n) = my(k=1); while (f(k) != n, k++); k; \\ Michel Marcus, Sep 10 2021
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CROSSREFS
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KEYWORD
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nonn,hard
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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