Pierce expansion of sech(1).

Terms

a(0) =1a(1) =2a(2) =3a(3) =8a(4) =9a(5) =24a(6) =37a(7) =85a(8) =1115a(9) =29153a(10) =423233a(11) =2208087a(12) =5102497a(13) =9813637a(14) =15922076a(15) =19204759a(16) =106559540a(17) =120015709a(18) =1493877142a(19) =2199074984a(20) =32818755269