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 A128646 #14 Feb 16 2025 08:33:05
%S A128646 1,2,4,12,60,10,80,720,7920,55440,55440,18480,18480,18480,425040,
%T A128646 5525520,160240080,53413360,160240080,160240080,480720240,480720240,
%U A128646 19709529840,19709529840,39419059680,197095298400,3350620072800
%N A128646 a(n) = denominator(Sum_{k=1..n} 1/(prime(k)-1)).
%C A128646 A120271(n) = numerator(Sum_{k=1..n} 1/(prime(k)-1)); A128648(n) = denominator(Sum_{k=1..n} (-1)^(k+1)/(prime(k)-1)); numbers m such that a(m) = A128648(m) are listed in A128649.
%H A128646 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PrimeSums.html">Prime Sums</a>
%F A128646 a(n) = denominator(Sum_{k=1..n} 1/(prime(k)-1)).
%t A128646 Table[Denominator[Sum[1/(Prime[k]-1),{k,1,n}]],{n,1,36}]
%Y A128646 Cf. A120271 (numerator(Sum_{k=1..n} 1/(prime(k)-1))).
%Y A128646 Cf. A128649, A128647, A128648 (denominator(Sum_{k=1..n} (-1)^(k+1)/(prime(k)-1))).
%Y A128646 Cf. A119686, A006093, A000040.
%K A128646 frac,nonn
%O A128646 1,2
%A A128646 _Alexander Adamchuk_, Mar 18 2007