Somos-4 variation with periodic coefficients.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =5a(6) =9a(7) =61a(8) =193a(9) =1439a(10) =13892a(11) =121853a(12) =1908467a(13) =47166783a(14) =675904139a(15) =39429369055