Genocchi numbers (of first kind): expansion of 2*x/(exp(x)+1).

Terms

a(0) =1a(1) =-1a(2) =0a(3) =1a(4) =0a(5) =-3a(6) =0a(7) =17a(8) =0a(9) =-155a(10) =0a(11) =2073a(12) =0a(13) =-38227a(14) =0a(15) =929569a(16) =0a(17) =-28820619a(18) =0a(19) =1109652905a(20) =0a(21) =-51943281731a(22) =0a(24) =0a(26) =0a(28) =0a(30) =0