A026689 a(n) = T(n,0) + T(n,1) + ... + T(n,[ n/2 ]), T given by A026681.

1, 1, 4, 6, 18, 27, 82, 138, 390, 644, 1837, 3242, 8835, 15271, 42086, 76403, 203377, 361636, 974089, 1802727, 4718991, 8559441, 22673687, 42562209, 110006420, 202537249, 529643894, 1005279834, 2572145945, 4791823354