An accelerator sequence for Catalan's constant.

Terms

a(0) =3a(1) =-1a(2) =5a(3) =-4a(4) =13a(5) =-16a(6) =38a(7) =-57a(8) =117a(9) =-193a(10) =370a(11) =-639a(12) =1186a(13) =-2094a(14) =3827a(15) =-6829a(16) =12389a(17) =-22220a(18) =40169a(19) =-72220a(20) =130338a(21) =-234609a(22) =423065a(23) =-761945a(24) =1373466a(25) =-2474291a(26) =4459278a(27) =-8034394a(28) =14478659a(29) =-26088169