a(n) = 5^n*sin(2n*arctan(1/2)) or numerator of tan(2n*arctan(1/2)).

A066770

a(n) = 5^n*sin(2n*arctan(1/2)) or numerator of tan(2n*arctan(1/2)).

Terms

    a(0) =4a(1) =24a(2) =44a(3) =-336a(4) =-3116a(5) =-10296a(6) =16124a(7) =354144a(8) =1721764a(9) =1476984a(10) =-34182196a(11) =-242017776a(12) =-597551756a(13) =2465133864a(14) =29729597084a(15) =116749235904a(16) =-42744511676

External references