at a premium vs deficient

at a premium

• At a high, or higher than expected, price. 

• Scarce, in short supply. 

• Above par value. 

deficient

• A person who is deficient. 

• Insufficient or inadequate in amount. 

• Lacking something essential; often construed with in. 

• Of a number n, Having the sum of divisors σ(n)<2n, or, equivalently, the sum of proper divisors (or aliquot sum) s(n).