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 A097250 #20 Apr 23 2017 23:55:53
%S A097250 1,4,12,60,420,4620,60060,1021020,19399380,446185740,12939386460,
%T A097250 401120980260,14841476269620,608500527054420,26165522663340060,
%U A097250 1229779565176982820,65178316954380089460,3845520700308425278140,234576762718813941966540,15716643102160534111758180
%N A097250 Smallest m such that A097249(m) = n; from n=1 onwards, twice the primorials, 2*A002110(n).
%C A097250 A097249(a(n))=n and A097249(m)<n for m<a(n).
%C A097250 a(n) = A088860(n) for n>=1. - _G. C. Greubel_, Apr 23 2017
%H A097250 Vincenzo Librandi, <a href="/A097250/b097250.txt">Table of n, a(n) for n = 0..200</a>
%H A097250 <a href="/index/Pri#primorial_numbers">Index entries for sequences related to primorial numbers</a>
%F A097250 a(n) = if n=0 then 1 else 2*A002110(n).
%t A097250 Join[{1}, 2 Denominator[Accumulate[1/Prime[Range[20]]]]] (* _Vincenzo Librandi_, Mar 25 2017 *)
%t A097250 Join[{1}, 2*FoldList[Times, 1, Prime[Range[50]]]] (* _G. C. Greubel_, Apr 23 2017 *)
%Y A097250 Cf. A002110, A088860, A097249.
%Y A097250 From a(1)=4 onwards, row 3 of A276945.
%K A097250 nonn
%O A097250 0,2
%A A097250 _Reinhard Zumkeller_, Aug 03 2004
%E A097250 Name amended by _Antti Karttunen_, Sep 24 2016
%E A097250 a(18)-a(19) from _Vincenzo Librandi_, Mar 25 2017