A087146 - OEIS

%I #12 Jul 12 2015 09:09:44

%S 1,2,3,5,9,13,14,17,27,28,33,39,103,115,205,291,1431,1532,1710,1937,

%T 3901,3981,4682,6569,20266,20662

%N Numbers n such that n!+(n+1)!-1 is prime.

%C 291 is in the sequence and also is in the sequence A087147, thus (291!+292!-1,291!+292!+1) is a twin pair of primes. Any additional terms are greater than 1800 with the next prime having more than 5086 digits.

%C a(27) > 25000. - _Robert Price_, Jul 12 2015

%C a(1)-a(26) give certified primes. - _Robert Price_, Jul 12 2015

%D H. Dubner, Factorial and primorial primes, J. Rec. Math., 19(No. 3, 1987)

%e 3 is in the sequence because 3!+4!-1=29 is prime.

%t v={}; Do[If[PrimeQ[n!+(n+1)!-1], v=Append[v, n]; Print[v]], {n, 1800}]; v

%Y Cf. A087147, A051856.

%K nonn

%O 1,2

%A _Farideh Firoozbakht_, Aug 19 2003

%E One more term from _Ryan Propper_, Aug 13 2005

%E a(21)-a(26) from _Robert Price_, Jul 12 2015