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 A217723 #36 May 23 2020 13:30:46
%S A217723 1,7,37,247,2557,32587,543097,10242787,233335657,6703028887,
%T A217723 207263519017,7628001653827,311878265181037,13394639596851067,
%U A217723 628284422185342477,33217442899375387207,1955977793053588026277,119244359152460559009547
%N A217723 a(n) = (sum of first n primorial numbers) minus 1.
%H A217723 Paul Larm (terms 1..20) and Amiram Eldar (terms 21..100), <a href="/A217723/b217723.txt">Table of n, a(n) for n = 1..100</a>
%H A217723 Paul Larm, <a href="/A217723/a217723_1.txt">Table of a(n) for n = 2..25</a> showing prime factors.
%F A217723 a(1) = P(1)# - 1, a(2) = P(1)# + P(2)# -1; where P(n)# is the product of first n prime numbers (primorial#).
%e A217723 For n = 4, a(4) = 2 + 2*3 + 2*3*5 + 2*3*5*7 - 1 = 247.
%t A217723 Accumulate[Denominator[Accumulate[1/Prime[Range[20]]]]] - 1 (* _Alonso del Arte_, Mar 21 2013 *)
%t A217723 Accumulate[Table[Fold[Times,Prime[Range[n]]],{n,20}]]-1 (* _Harvey P. Dale_, May 23 2020 *)
%Y A217723 Equals A060389 - 1. Cf. A223546, A223548.
%K A217723 nonn,easy
%O A217723 1,2
%A A217723 _Paul Larm_, Mar 21 2013