Calculating $\sqrt{28\cdot 29 \cdot 30\cdot 31+1}$ Is it possible to calculate $\sqrt{28 \cdot 29 \cdot 30 \cdot 31 +1}$ without any kind of electronic aid?
I tried to factor it using equations like $(x+y)^2=x^2+2xy+y^2$ but it didn't work.

One notes in base 28, that the numbers are 1.0, 1.1, 1.2, 1.3.  The product of the inner and outer pairs are 1.3.0 and 1.3.2.  Adding one to this product gives $1.3.1^2$, whence the square root is 1.3.1.  
Evaluating this in decimal gives 869.
When this series starts with 35, the result is the cube 1331.
