Least value x solving x^2 - y^2 = n!

Terms

a(0) =5a(1) =11a(2) =27a(3) =71a(4) =201a(5) =603a(6) =1905a(7) =6318a(8) =21888a(9) =78912a(10) =295260a(11) =1143536a(12) =4574144a(13) =18859680a(14) =80014848a(15) =348776640a(16) =1559776320a(17) =7147792848a(18) =33526120320a(19) =160785625902a(20) =787685472000