a(n) = ((1 + sqrt(n))^n - (1 - sqrt(n))^n)/(2*n*sqrt(n)).

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =16a(5) =57a(6) =232a(7) =1017a(8) =4864a(9) =24641a(10) =133024a(11) =752765a(12) =4476928a(13) =27707513a(14) =178613376a(15) =1191756593a(16) =8231124992a(17) =58598528065a(18) =429868937728