Successive denominators of Wallis's approximation to Pi/2 (reduced).

Terms

a(0) =1a(1) =1a(2) =3a(3) =9a(4) =45a(5) =75a(6) =175a(7) =1225a(8) =11025a(9) =19845a(10) =43659a(11) =160083a(12) =693693a(13) =1288287a(14) =2760615a(15) =41409225a(16) =703956825a(17) =1329696225a(18) =2807136475a(19) =10667118605a(20) =44801898141a(21) =85530896451a(22) =178837328943