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 A274385 #8 Sep 08 2022 08:46:17 %S A274385 2,3,7,47,383,10321919,51011754393599, %T A274385 1130138339199322632554990773529330319359999999, %U A274385 73562883979319395645666688474019139929848516028923903999999999,4208832729023498248022825567687608993477547383960134557368319999999999 %N A274385 Double factorial primes: primes which are within 1 of a double factorial number. %H A274385 Wikipedia, <a href="http://en.wikipedia.org/wiki/Double_factorial">Double factorial</a> %H A274385 <a href="/index/Fa#factorial">Index entries for sequences related to factorial numbers</a> %e A274385 a(2) = 3 = 2 + 1 = 2!! + 1 is the 2nd prime of that form. %e A274385 a(4) = 47 = 2*4*6 - 1 = 6!! - 1 is the 4th prime of that form. %o A274385 (Magma) r:=91; I:=[1, 1]; lst1:=[n le 2 select I[n] else (n-1)*Self(n-2): n in [1..r]]; lst2:=[]; for c in [1..r] do a:=lst1[c]; for s in [-1..1 by 2] do p:=a+s; if IsPrime(p) and not p in lst2 then Append(~lst2, p); end if; end for; end for; lst2; %Y A274385 Cf. A006882, A007749, A080778, A117141. %K A274385 nonn %O A274385 1,1 %A A274385 _Arkadiusz Wesolowski_, Jun 19 2016