LDI - Load Immediate
Description: Loads an 8 bit constant directly to register 16 to 31.
To encode a value of 16-31, you only need 4 bits (3-0) if you assume bit 4 to always be 1.
In your case, the encoding would be;
1110 0011 0110 1101 (where dddd is 6 since 16 + 6 = 22)