设这四个连续整数,从小到大依次为n,n+1,n+2,n+3
n(n+1)(n+2)(n+3)
=(n^2+3n)(n^2+8n+2)
=(n^2+3n+1)^2-1
n(n+1)(n+2)(n+3)+1
=(n^2+3n+1)^2
∴四个连续整数的乘积加上1,是一完全平方数