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 A120284 #6 Sep 14 2024 02:23:27
%S A120284 3,9,25,125,147,343,761,6849,7381,81191,86021,1118273,1171733,1171733,
%T A120284 2436559,41421503,42822903,271211719,279175675,55835135,19093197,
%U A120284 439143531,1347822955,33695573875,34395742267,309561680403,315404588903
%N A120284 Numerator of absolute value of Sum_{k=1..n} (-1)^(k+1)*(2*k+1)*(Sum_{i=1..k} 1/i).
%C A120284 p^3 divides a(p-1) for prime p>3, a(p-1)/p^3=A061002[n], a(p-1)/p=A001008(p-1) for p>2. p^2 divides a(p-2) for prime p>3. p^3 divides a(p^2-1) for prime p>3. p divides a(p^2-2) for prime p>3. p^3 divides a(p^3-1) for prime p>3. p^3 divides a(p^4-1) for prime p>3.
%F A120284 a(n) = numerator(abs(Sum_{k=1..n} (-1)^(k+1)*(2*k+1)*(Sum_{i=1..k} 1/i))).
%t A120284 Numerator[Abs[Table[Sum[(-1)^(k+1)*(2k+1)*Sum[1/i,{i,1,k}],{k,1,n}],{n,1,30}]]]
%Y A120284 Cf. A061002, A001008.
%K A120284 frac,nonn
%O A120284 1,1
%A A120284 _Alexander Adamchuk_, Jul 07 2006