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A265765
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Numerators of primes-only best approximates (POBAs) to 4; see Comments.
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2
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11, 7, 13, 11, 19, 29, 43, 53, 67, 149, 163, 173, 211, 269, 283, 293, 317, 331, 389, 509, 523, 547, 557, 653, 691, 773, 787, 797, 907, 1051, 1109, 1123, 1171, 1229, 1493, 1531, 1637, 1723, 1733, 1867, 1949, 1997, 2011, 2083, 2251, 2309, 2347, 2371, 2467
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OFFSET
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1,1
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COMMENTS
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Suppose that x > 0. A fraction p/q of primes is a primes-only best approximate (POBA), and we write "p/q in B(x)", if 0 < |x - p/q| < |x - u/v| for all primes u and v such that v < q, and also, |x - p/q| < |x - p'/q| for every prime p' except p. Note that for some choices of x, there are values of q for which there are two POBAs. In these cases, the greater is placed first; e.g., B(3) = (7/2, 5/2, 17/5, 13/5, 23/7, 19/7, ...). See A265759 for a guide to related sequences.
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LINKS
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EXAMPLE
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The POBAs for 4 start with 11/2, 7/2, 13/3, 11/3, 19/5, 29/7, 43/11, 53/13, 67/17. For example, if p and q are primes and q > 13, then 53/13 is closer to 3 than p/q is.
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MATHEMATICA
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x = 4; z = 200; p[k_] := p[k] = Prime[k];
t = Table[Max[Table[NextPrime[x*p[k], -1]/p[k], {k, 1, n}]], {n, 1, z}];
d = DeleteDuplicates[t]; tL = Select[d, # > 0 &] (* lower POBA *)
t = Table[Min[Table[NextPrime[x*p[k]]/p[k], {k, 1, n}]], {n, 1, z}];
d = DeleteDuplicates[t]; tU = Select[d, # > 0 &] (* upper POBA *)
v = Sort[Union[tL, tU], Abs[#1 - x] > Abs[#2 - x] &];
b = Denominator[v]; s = Select[Range[Length[b]], b[[#]] == Min[Drop[b, # - 1]] &];
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CROSSREFS
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KEYWORD
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nonn,frac
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AUTHOR
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STATUS
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approved
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