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 A090704 #28 Jun 14 2025 07:13:49 %S A090704 2,3,5,7,8,11,27,77,98,183,285,290,397,410,599,717,731,888,1962,2239, %T A090704 2241,2532,8799,11402,18334,20276,21028 %N A090704 Numbers k such that k*k! - 1 is prime. %F A090704 a(n) = A049433(n) - 1 because n! - (n-1)! - 1 = (n-1)*(n-1)! - 1. %e A090704 5 is a term since 5*5! - 1 = 599 is prime. %t A090704 Select[Range[2600],PrimeQ[#(#!)-1]&] (* Because a(22) generates a 7524 digit number to be tested for primality, the program takes a long time to run. *) (* _Harvey P. Dale_, May 27 2014 *) %Y A090704 Cf. A049433. %K A090704 nonn,more %O A090704 1,1 %A A090704 Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Jan 15 2004 %E A090704 More terms from _Farideh Firoozbakht_, Oct 31 2004 %E A090704 a(23)-a(24) using A049433 from _Michel Marcus_, May 29 2014 %E A090704 a(25)-a(27) from _Michael S. Branicky_, Jun 13 2025