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A265815 Denominators of lower primes-only best approximates (POBAs) to e; see Comments.

%I A265815 #10 Jul 21 2022 01:53:28
%S A265815 2,5,7,113,163,227,823,887,1093,2179,2591,2797,4373,4657,5651,8867,
%T A265815 27673,32749,47189,104459,155723,430061,583853,673297,1126523,1869173,
%U A265815 3120317,3445919,8341961,24681191,26349383,70271051,77869361,81514259,89910487,157461181,533931763,583892083,770930497
%N A265815 Denominators of lower primes-only best approximates (POBAs) to e; see Comments.
%C A265815 Suppose that x > 0. A fraction p/q of primes is a lower primes-only best approximate, and we write "p/q is in L(x)", if u/v < p/q < x < p'/q for all primes u and v such that v < q, where p' is least prime > p.
%C A265815 Let q(1) be the least prime q such that u/q < x for some prime u, and let p(1) be the greatest such u. The sequence L(x) follows inductively: for n > 1, let q(n) is the least prime q such that p(n)/q(n) < p/q < x for some prime p. Let q(n+1) = q and let p(n+1) be the greatest prime p such that p(n)/q(n) < p/q < x.
%C A265815 For a guide to POBAs, lower POBAs, and upper POBAs, see A265759.
%e A265815 The lower POBAs to e; start with 5/2, 13/5, 19/7, 307/113, 443/163, 617/227, 2237/823. For example, if p and q are primes and q > 823, and p/q < e, then 2237/823 is closer to e than p/q is.
%t A265815 x = E; z = 1000; p[k_] := p[k] = Prime[k];
%t A265815 t = Table[Max[Table[NextPrime[x*p[k], -1]/p[k], {k, 1, n}]], {n, 1, z}];
%t A265815 d = DeleteDuplicates[t]; tL = Select[d, # > 0 &] (* lower POBA *)
%t A265815 t = Table[Min[Table[NextPrime[x*p[k]]/p[k], {k, 1, n}]], {n, 1, z}];
%t A265815 d = DeleteDuplicates[t]; tU = Select[d, # > 0 &] (* upper POBA *)
%t A265815 v = Sort[Union[tL, tU], Abs[#1 - x] > Abs[#2 - x] &];
%t A265815 b = Denominator[v]; s = Select[Range[Length[b]], b[[#]] == Min[Drop[b, # - 1]] &];
%t A265815 y = Table[v[[s[[n]]]], {n, 1, Length[s]}] (* POBA, A265818/A265819 *)
%t A265815 Numerator[tL]   (* A265814 *)
%t A265815 Denominator[tL] (* A265815 *)
%t A265815 Numerator[tU]   (* A265816 *)
%t A265815 Denominator[tU] (* A265817 *)
%t A265815 Numerator[y]    (* A265818 *)
%t A265815 Denominator[y]  (* A265819 *)
%Y A265815 Cf. A000040, A265759, A265814, A265816, A265817, A265818, A265819.
%K A265815 nonn,frac
%O A265815 1,1
%A A265815 _Clark Kimberling_, Jan 02 2016
%E A265815 More terms from _Bert Dobbelaere_, Jul 21 2022