a(n) = Numerator([x^n] (4*sinh(sqrt(x)/2)^2*cosh(sqrt(x)))/x).

Terms

a(0) =1a(1) =7a(2) =31a(3) =127a(4) =73a(5) =2047a(6) =8191a(7) =4681a(8) =131071a(9) =524287a(10) =42799a(11) =8388607a(12) =33554431a(13) =19173961a(14) =536870911a(15) =2147483647a(16) =53353631a(17) =1108378657a(18) =137438953471a(19) =78536544841a(22) =162139963543