a(n) = lcm(1, 2, ..., 2n) / lcm(1, 2, ..., n).

Terms

a(0) =1a(1) =2a(2) =6a(3) =10a(4) =70a(5) =42a(6) =462a(7) =858a(8) =858a(9) =4862a(10) =92378a(11) =8398a(12) =193154a(13) =74290a(14) =222870a(15) =6463230a(16) =200360130a(17) =11785890a(18) =11785890a(19) =22951470a(20) =22951470a(21) =941010270a(22) =40463441610a(23) =1759280070a(24) =82686163290a(25) =115760628606a(26) =115760628606