Number of ways to put n red and n blue balls into n indistinguishable boxes.

Terms

a(0) =1a(1) =1a(2) =5a(3) =19a(4) =74a(5) =248a(6) =814a(7) =2457a(8) =7168a(9) =19928a(10) =53688a(11) =139820a(12) =354987a(13) =878434a(14) =2128102a(15) =5052010a(16) =11781881a(17) =27019758a(18) =61035671a(19) =135928105a(20) =298784144a(21) =648726349a(22) =1392474574a(23) =2956730910a(24) =6214668074a(25) =12937060340a(26) =26686392239a(27) =54572423946a(28) =110680119454a(29) =222710856175