Amines with an odd number of atoms give an odd molecular ion in their mass spectra.

Amines with an odd number of Nitrogen atoms give an odd molecular ion in their mass spectra.

I have attached four examples of such amines, 

Amines containg 1 and 3 number of Nitrogen Atoms give Odd Molecular Ion in their Mass spectra. 
And,
Amines containg 2 and 4 number of Nitrogen Atoms give Even Molecular Ion in their Mass spectra.