This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A232180 #20 Jul 17 2025 14:48:51
%S A232180 1,11,137,363,7129,83711,1145993,1195757,42142223,275295799,18858053,
%T A232180 444316699,34052522467,312536252003,9227046511387,290774257297357,
%U A232180 53676090078349,54437269998109,2040798836801833,2066035355155033,85691034670497533
%N A232180 First bisection of harmonic numbers (numerators).
%C A232180 Numerator of H(2*n-1), where H(n) = Sum_{k=1..n} 1/k.
%C A232180 It can be noted that the second row of the Akiyama-Tanigawa transform of the fractions A232180/A232181 has a simple expression: -5/6, -9/10, -13/14, -17/18, -21/22, ... are of the form -(4*k+5)/(4*k+6).
%F A232180 a(n) ~ exp(2n).
%t A232180 a[n_] := HarmonicNumber[2*n-1] // Numerator; Table[a[n], {n, 1, 25}]
%o A232180 (Magma) [Numerator(HarmonicNumber(2*n-1)): n in [1..30]]; // _Bruno Berselli_, Nov 20 2013
%Y A232180 Cf. A001008, A002547, A093158, A175441, A232181 (denominators).
%K A232180 nonn,frac,easy
%O A232180 1,2
%A A232180 _Jean-François Alcover_ and _Paul Curtz_, Nov 20 2013