a(n) =(A001359[n]^2-1)/2.

Terms

a(0) =2a(1) =6a(2) =30a(3) =72a(4) =210a(5) =420a(6) =870a(7) =1260a(8) =2550a(9) =2862a(10) =4692a(11) =5550a(12) =8010a(13) =9120a(14) =9702a(15) =12882a(16) =14280a(17) =18090a(18) =19740a(19) =24180a(20) =30102a(21) =43890a(22) =46440a(23) =53130a(24) =67860a(25) =80940a(26) =89700a(27) =95172a(28) =102720a(29) =108570