a(n) = floor((Pi^2/6)^n).

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =7a(5) =12a(6) =19a(7) =32a(8) =53a(9) =88a(10) =145a(11) =238a(12) =392a(13) =645a(14) =1061a(15) =1746a(16) =2873a(17) =4726a(18) =7774a(19) =12788a(20) =21036a(21) =34603a(22) =56920a(23) =93630a(24) =154015a(25) =253345a(26) =416735a(27) =685503a(28) =1127607a(29) =1854839