a(n) = floor(cosh(n+1) - cosh(n)).

Terms

a(0) =0a(1) =2a(2) =6a(3) =17a(4) =46a(5) =127a(6) =346a(7) =942a(8) =2561a(9) =6961a(10) =18923a(11) =51440a(12) =139829a(13) =380095a(14) =1033206a(15) =2808546a(16) =7634421a(17) =20752508a(18) =56411165a(19) =153341447a(20) =416825269a(21) =1133048555a(22) =3079945300a(23) =8372159341a(24) =22757888603a(25) =61862355045a(26) =168159315586a(27) =457104411844