Self-convolution of A257889.

Terms

a(0) =1a(1) =2a(2) =5a(3) =14a(4) =34a(5) =96a(6) =261a(7) =692a(8) =1680a(9) =4540a(10) =12540a(11) =34552a(12) =92728a(13) =251572a(14) =662340a(15) =1729628a(16) =4261528a(17) =11130160a(18) =29802200a(19) =80103640a(20) =218398544a(21) =595050400a(22) =1621285648a(23) =4411577744a(24) =11776668772a(25) =31899937136a(26) =85998657296a(27) =231056788736a(28) =607876418544