A347669 Indices of first occurrences of n in A347409.

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

Offset

0,2

Links

Table of n, a(n) for n=0..35.

Index entries for sequences related to 3x+1 (or Collatz) problem

Example

a(5) = 15 because 5 occurs for the first time at position 15 in A347409.

Mathematica

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}]

Prog

(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

Crossrefs

Cf. A006370, A070165, A135282, A347409, A347668.

Sequence in context: A277272 A109588 A254788 * A352812 A052331 A242365

Adjacent sequences: A347666 A347667 A347668 * A347670 A347671 A347672

Keyword

nonn,hard

Author

Paolo Xausa, Sep 10 2021

Extensions

a(21)-a(22) from Michel Marcus, Sep 10 2021

a(23)-a(28) from Alois P. Heinz, Sep 11 2021

a(29)-a(34) from Michael S. Branicky, Sep 28 2021

a(35) from Chai Wah Wu, Oct 02 2021

Status

approved