数学双沟47

doctortt

n = x^3 - 1

n = a + (a+1) + (a+2) + (a+3)

x^3 - 1 = a + (a+1) + (a+2) + (a+3)

x^3 = 4a + 7

1) 100<n<1000,  7^3 works

2)  
            n<400, 7^3 and 4^3 - no good

Answer is A.