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A265818 Numerators of primes-only best approximates (POBAs) to e; see Comments. 7

%I #16 Jul 21 2022 01:53:43

%S 7,5,13,19,193,7043,7603,11251,15149,15361,17291,24103,46643,49171,

%T 3062207,5080939,8481901,8823377,22675801,63342553,67090433,71625049,

%U 142362299,221578729,244402043,428023867,1293881119,1587183239,2095606361,3221097589,3905501983,4072807391,14649723833

%N Numerators of primes-only best approximates (POBAs) to e; see Comments.

%C 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 POBA's. 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. Many terms of A265806 are also terms of A265801 (denominators of POBAs to tau).

%e The POBAs to Pi start with 7/2, 5/2, 13/5, 19/7, 193/71, 7043/2591, 7603/2797. For example, if p and q are primes and q > 2591, then 7043/2591 is closer to e than p/q is.

%t x = E; z = 1000; p[k_] := p[k] = Prime[k];

%t t = Table[Max[Table[NextPrime[x*p[k], -1]/p[k], {k, 1, n}]], {n, 1, z}];

%t d = DeleteDuplicates[t]; tL = Select[d, # > 0 &] (* lower POBA *)

%t t = Table[Min[Table[NextPrime[x*p[k]]/p[k], {k, 1, n}]], {n, 1, z}];

%t d = DeleteDuplicates[t]; tU = Select[d, # > 0 &] (* upper POBA *)

%t v = Sort[Union[tL, tU], Abs[#1 - x] > Abs[#2 - x] &];

%t b = Denominator[v]; s = Select[Range[Length[b]], b[[#]] == Min[Drop[b, # - 1]] &];

%t y = Table[v[[s[[n]]]], {n, 1, Length[s]}] (* POBA, A265818/A265819 *)

%t Numerator[tL] (* A265814 *)

%t Denominator[tL] (* A265815 *)

%t Numerator[tU] (* A265816 *)

%t Denominator[tU] (* A265817 *)

%t Numerator[y] (* A265818 *)

%t Denominator[y] (* A265819 *)

%Y Cf. A000040, A265759, A265814, A265815, A265816, A265817, A265819.

%K nonn,frac

%O 1,1

%A _Clark Kimberling_, Jan 06 2016

%E More terms from _Bert Dobbelaere_, Jul 21 2022

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Last modified March 28 08:22 EDT 2024. Contains 371236 sequences. (Running on oeis4.)