%I #8 Sep 08 2022 08:46:17

%S 2,3,7,47,383,10321919,51011754393599,

%T 1130138339199322632554990773529330319359999999,

%U 73562883979319395645666688474019139929848516028923903999999999,4208832729023498248022825567687608993477547383960134557368319999999999

%N Double factorial primes: primes which are within 1 of a double factorial number.

%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Double_factorial">Double factorial</a>

%H <a href="/index/Fa#factorial">Index entries for sequences related to factorial numbers</a>

%e a(2) = 3 = 2 + 1 = 2!! + 1 is the 2nd prime of that form.

%e a(4) = 47 = 2*4*6 - 1 = 6!! - 1 is the 4th prime of that form.

%o (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 Cf. A006882, A007749, A080778, A117141.

%K nonn

%O 1,1

%A _Arkadiusz Wesolowski_, Jun 19 2016