<Dd> r 4 (n) = 8 σ (n) − 32 σ (n / 4), (\ displaystyle r_ (4) (n) = 8 \ sigma (n) - 32 \ sigma (n / 4) \,) </Dd> <P> where the second term is to be taken as zero if n is not divisible by 4 . In particular, for a prime number p we have the explicit formula r (p) = 8 (p + 1). </P> <P> Some values of r (n) occur infinitely often as r (n) = r (2 n) whenever n is even . The values of r (n) / n can be arbitrarily large: indeed, r (n) / n is infinitely often larger than 8 √ log n . </P> <P> The sequence of positive integers which have only one representation as a sum of four squares (up to order) is: </P>

How do we express four less than the square of a number