cp's OEIS Frontend

A340737 Numerators of a sequence of fractions converging to e.

%I A340737 #24 Feb 13 2021 15:06:58
%S A340737 3,5,19,49,193,685,2721,12341,49171,271801,1084483,7073725,28245729,
%T A340737 212385209,848456353,7226001865,28875761731,274743964621,
%U A340737 1098127402131,11544775603241,46150226651233,531276670190245,2124008553358849,26573182030311229,106246577894593683,1435390805853694145
%N A340737 Numerators of a sequence of fractions converging to e.
%C A340737 This sequence is a subset of the numerators of a sequence of fractions converging to e which was obtained by the use of a program which searched for a fraction having a closer value to e than the preceding one. The initial terms of this sequence were 3/1, 5/2, 8/3, 11/4, 19/7, 49/18, 68/25, 87/32, 106/39, 193/71, 685/252, 878/323, 1071/394, 1264/465, 1457/536, 2721/1001, 12341/4540. The subset of the numerators filtered out of this sequence are a(1)..a(8).
%C A340737 The convergence is conjectured.
%F A340737 a(1) = 3, a(2) = 5; for n > 2, a(n) = (n+2)*a(n-1)/2 - a(n-2) - (n-2)*a(n-3)/2 if n is even, 2*a(n-1) + n*a(n-2) otherwise.
%e A340737 Sequence of fractions begins 3/1, 5/2, 19/7, 49/18, 193/71, 685/252, 2721/1001, 12341/4540, ...
%p A340737 e:=proc(a,b,n)option remember; e(a,b,1):=a; e(a,b,2):=b; if n>2 and n mod 2 =1 then 2*e(a,b,n-1)+n*e(a,b,n-2) else if n>3 and n mod 2 = 0 then (n+2)*e(a,b,n-1)/2 -(e(a,b,n-2)+(n-2)*e(a,b,n-3)/2) fi fi end
%p A340737 seq(e(3,5,n), n = 1..20)
%p A340737 # code to print the sequence of fractions and error
%p A340737 for n from 1` to 20 do print(e(3,5,n)/e(1,2,n), evalf(exp(1)-e(3,5,n)/e(1,2,n)) od
%t A340737 a[1] = 3; a[2] = 5; a[n_] := a[n] = If[EvenQ[n], (n + 2)*a[n - 1]/2 - (a[n - 2] + (n - 2)*a[n - 3]/2), 2*a[n - 1] + n*a[n - 2]]; Array[a, 20] (* _Amiram Eldar_, Jan 18 2021 *)
%Y A340737 Denominators are listed in A340738.
%Y A340737 Cf. A007676/A007677.
%K A340737 nonn,frac
%O A340737 1,1
%A A340737 _Gary Detlefs_, Jan 18 2021