a(n) = Sum_{k=0..floor(n/2)} (-1)^k * binomial(4*n-2*k,n-2*k).
A390687
a(n) = Sum_{k=0..floor(n/2)} (-1)^k * binomial(4*n-2*k,n-2*k).
Terms
- a(0) =1a(1) =4a(2) =27a(3) =210a(4) =1730a(5) =14704a(6) =127470a(7) =1120262a(8) =9944676a(9) =88961008a(10) =800658947a(11) =7241596046a(12) =65764261576a(13) =599284477328
External references
- oeis: A390687