a(n) = Sum_{k=0..n} 2^binomial(n,k).A001315a(n) = Sum_{k=0..n} 2^binomial(n,k).Terms a(0) =2a(1) =4a(2) =8a(3) =20a(4) =100a(5) =2116a(6) =1114244a(7) =68723671300External referencesoeis: A001315