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 A282512 #27 Dec 15 2017 22:17:24
%S A282512 1,4,12,24,72,360,360,2520,504,1008,336,1680,1680,18480,18480,92400,
%T A282512 1201200,10810800,10810800,10810800,21621600,21621600,367567200,
%U A282512 52509600,52509600,997682400,997682400,997682400,6983776800,6983776800,6983776800,160626866400,160626866400,1124388064800,1124388064800
%N A282512 Denominator of the sum of the reciprocals of the first n nonprimes.
%H A282512 Robert Israel, <a href="/A282512/b282512.txt">Table of n, a(n) for n = 1..3954</a>
%e A282512 The first few fractions are 1, 5/4, 17/12, 37/24, 119/72, 631/360, 661/360, 4807/2520, 995/504, 2053/1008, 703/336, 3599/1680, ... - _N. J. A. Sloane_, Dec 15 2017
%p A282512 NP:= remove(isprime, [$1..100]):
%p A282512 S:= ListTools:-PartialSums(map(t -> 1/t, NP)):
%p A282512 map(denom, S); # _Robert Israel_, May 01 2017
%t A282512 With[{nn=50}, Denominator@Accumulate[1/Complement[Range@nn, Prime@Range@PrimePi@nn]]] (* _Vincenzo Librandi_, May 02 2017 *)
%Y A282512 Cf. A018252 (nonprime numbers), A282511 (numerators).
%Y A282512 The following fractions are all related to each other: Sum 1/n: A001008/A002805, Sum 1/prime(n): A024451/A002110 and A106830/A034386, Sum 1/nonprime(n): A282511/A282512, Sum 1/composite(n): A250133/A296358.
%K A282512 nonn,frac
%O A282512 1,2
%A A282512 _Ralf Steiner_, Feb 17 2017
%E A282512 Corrected by _Robert Israel_, May 01 2017