Main diagonal of A274637.

Terms

a(0) =0a(1) =0a(2) =3a(3) =5a(4) =15a(5) =27a(6) =63a(7) =119a(8) =255a(9) =495a(10) =1023a(11) =2015a(12) =4095a(13) =8127a(14) =16383a(15) =32639a(16) =65535a(17) =130815a(18) =262143a(19) =523775a(20) =1048575a(21) =2096127a(22) =4194303a(23) =8386559a(24) =16777215a(25) =33550335a(26) =67108863a(27) =134209535a(28) =268435455a(29) =536854527