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 A119955 #6 Feb 16 2025 08:33:01
%S A119955 1,2,3,4,5,9,10,11,12,13,14,27,49,50,51,52,53,125,126,127,128,129,130,
%T A119955 131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146,147,
%U A119955 148,149,150,151,152,153,154,155,289,290,291,292,293,841,842,843,844
%N A119955 Numbers n such that denominator of n-th Harmonic Number equals denominator of n-th Alternative Harmonic Number.
%C A119955 Up to n=14 A002805[n] coincides with A058312[n]. a(n) up to a(12)=27 coincides with A096304[n].
%H A119955 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/HarmonicNumber.html">Harmonic Number</a>.
%e A119955 Denominators of Harmonic Number (H[n] = Sum[1/i, {i, n}]) are A002805[n] = {1,2,6,12,60,20,140,280,2520,2520,27720,27720,360360,360360,360360,...}.
%e A119955 Denominators of Alternative Harmonic Number (H'[n] = Sum[(-1)^(i+1)*1/i, {i, n}]) are A058312[n] = {1,2,6,12,60,60,420,840,2520,2520,27720,27720,360360,360360,72072,...}.
%e A119955 a(1) = 1 because A002805[1] = A058312[1].
%e A119955 15 is not in a(n) because A002805[15] = 360360 is not equal to A058312[15] = 72072.
%t A119955 Do[s1=Denominator[Sum[(-1)^(i+1)*1/i, {i, n}]]; s2=Denominator[Sum[1/i, {i, n}]]; If[Equal[s2, s1], Print[n]], {n, 1, 1500}]
%Y A119955 Cf. A002805, A058312, A096304.
%K A119955 nonn
%O A119955 1,2
%A A119955 _Alexander Adamchuk_, Aug 02 2006