a(n) = numerator(4^(n + 1)*zeta(-n, 1/4)).

Terms

a(0) =1a(1) =1a(2) =-1a(3) =-7a(4) =5a(5) =31a(6) =-61a(7) =-127a(8) =1385a(9) =511a(10) =-50521a(11) =-1414477a(12) =2702765a(13) =8191a(14) =-199360981a(15) =-118518239a(16) =19391512145a(17) =5749691557a(19) =-91546277357a(21) =162912981133