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 A217651 #8 May 16 2021 01:55:45
%S A217651 3,5,7,19,1759,192684799,14285134079,145284339199,509122178611199,
%T A217651 53165268316159999,253515360530431999,
%U A217651 89312661819089868632723554303999999,25863781053916181957690694149957243371519999999
%N A217651 Primes of the form 2*k!!! - 1.
%C A217651 k!!! is a triple factorial number (see the definition in A007661).
%C A217651 The corresponding k are in A217650.
%e A217651 19 is in the sequence because k = 5 => 2*5!!! - 1 = 2*10 - 1 = 19 is prime.
%p A217651 A:= n -> mul(k, k = select(k -> k mod 3 = n mod 3, [$1 .. n])): for p from 0 to 200 do:if type(2*A(p)-1,prime)=true then printf(`%d, `,2*A(p)-1):else fi:od:
%t A217651 multiFactorial[n_, k_] := If[n < 1, 1, If[n < k + 1, n, n*multiFactorial[n - k, k]]];
%t A217651 Select[Table[2*multiFactorial[n, 3] - 1, {n, 0, 60}], PrimeQ]
%Y A217651 Cf. A007661, A217650, A217648.
%K A217651 nonn
%O A217651 1,1
%A A217651 _Michel Lagneau_, Oct 09 2012