Curve256189 is defined over
It has
Its twist has
Curve256189 has the same security properties as Curve25519 [1]. Note that with A = 61370 we have (A-2)/4 = 15342 is small. As described in [1], this provides speed benefits in implementations.
Note that there is no reason to use Curve256189 over Curve25519, generating this curve was done pure for educational purposes.
[1] D. J. Bernstein. Curve25519: new Diffie-Hellman speed records. Proceedings of PKC 2006, pp. 207-228.