a(n) = Sum_{d|n} binomial(n,d)*binomial(n,n/d).

Terms

a(0) =1a(1) =4a(2) =6a(3) =44a(4) =10a(5) =612a(6) =14a(7) =3936a(8) =7074a(9) =22700a(10) =22a(11) =339792a(12) =26a(13) =624652a(14) =2732760a(15) =6401232a(16) =34a(17) =45174204a(18) =38a(19) =220441080a(20) =309304842a(21) =325909628a(22) =46a(23) =7330314960a(24) =2822796950a(25) =6760390052a(26) =27417926304a(27) =78814587656a(28) =58a(29) =548150764560