A027171 a(n) = A027170(2n, n).
1, 10, 42, 156, 570, 2096, 7784, 29168, 110106, 418128, 1595616, 6113740, 23505352, 90633796, 350351636, 1357278296, 5268292826, 20483876816, 79765662896, 311038321436, 1214362277696, 4746455801876, 18570960418916
Offset: 0