a(n) = (1/2) * Sum_{k=0..floor(n/3)} 2^(n-2*k) * binomial(2*n-4*k+2,2*k+1).
A387602
a(n) = (1/2) * Sum_{k=0..floor(n/3)} 2^(n-2*k) * binomial(2*n-4*k+2,2*k+1).
Terms
- a(0) =1a(1) =4a(2) =12a(3) =36a(4) =120a(5) =416a(6) =1420a(7) =4768a(8) =15968a(9) =53664a(10) =180736a(11) =608640a(12) =2048336a(13) =6891968a(14) =23191104a(15) =78044352a(16) =262644608a(17) =883866624a(18) =2974400960a(19) =10009502720a(20) =33684265984a(21) =113355412480a(22) =381467226112
External references
- oeis: A387602