Numerator of Sum_{i=0..n} (-1)^i*4/(2*i + 1).

Terms

a(0) =4a(1) =8a(2) =52a(3) =304a(4) =1052a(5) =10312a(6) =147916a(7) =135904a(8) =2490548a(9) =44257352a(10) =47028692a(11) =1023461776a(12) =5385020324a(13) =15411418072a(14) =467009482388