Numerator of Sum_{k=0..n} (-1)^k/(3*k+1).

Terms

a(0) =1a(1) =3a(2) =25a(3) =111a(4) =1583a(5) =5877a(6) =118943a(7) =1239213a(8) =6500369a(9) =6228669a(10) =200696339a(11) =3293919963a(12) =125884243831a(13) =122175729021