Cos(a(n)) decreases monotonically to -1.

Terms

a(0) =1a(1) =2a(2) =3a(3) =22a(4) =355a(5) =104348a(6) =208341a(7) =521030a(8) =833719a(9) =1146408a(10) =5419351a(11) =85563208a(12) =165707065a(13) =245850922a(14) =657408909a(15) =1068966896a(16) =3618458675a(17) =6167950454a(18) =21053343141