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 A161672 #6 Mar 22 2022 17:51:18 %S A161672 0,3,10,21,3960,77220,490089600,1523733120,2075793350400, %T A161672 50710801232931840000,3144069676441774080000, %U A161672 19348101737674447004467200000,137500509682406403378413568000000 %N A161672 Half the product of all numbers from A141468(n) up to prime(n). %H A161672 Michael De Vlieger, <a href="/A161672/b161672.txt">Table of n, a(n) for n = 1..99</a> %F A161672 a(n) = prime(n)!/ (2*(A141468(n)-1)!). %e A161672 a(1)=0 is the product 0*1*2/2. a(2) is the product 1*2*3/2 = 3. a(3)=10 is the product 4*5/2. %t A161672 f[n_] := FixedPoint[n + PrimePi@ # &, n + PrimePi@ n]; Array[1/2*Times @@ Range[f[# - 1], Prime[#]] &, 13] (* _Michael De Vlieger_, Mar 22 2022, after _Robert G. Wilson v_ at A141468 *) %Y A161672 Cf. A000040, A141468. %K A161672 nonn %O A161672 1,2 %A A161672 _Juri-Stepan Gerasimov_, Jun 16 2009 %E A161672 a(0) replaced by 0 - _R. J. Mathar_, May 21 2010