Denominator of Sum_{k=0..n} (-1)^k / (2*k+1).

Terms

a(0) =1a(1) =3a(2) =15a(3) =105a(4) =315a(5) =3465a(6) =45045a(7) =45045a(8) =765765a(9) =14549535a(10) =14549535a(11) =334639305a(12) =1673196525a(13) =5019589575a(14) =145568097675