Standard form of a number : Standard form of a number $N\left(>1\right)$  is $N=P_1{}^{n_1},P_2{}^{n_2},P_3{}^{n_3}\mathrm{......}{P}_k{}^{n_k}$  where $P_1,P_2,P_3,\mathrm{....}{P}_k$  are distinct primes $n_1,n_2,\mathrm{......}{n}_k$  are positive integers.

Number of divisors of a natural number : If $N=P_1{}^{n_1},P_2{}^{n_2},P_3{}^{n_3}\mathrm{......}{P}_k{}^{n_k}$  then number of divisors of  $N,d\left(N\right)=\left(n_1+1\right)\left(n_2+1\right)\mathrm{......}\left(n_k+1\right)$ .

Sum of divisors of natural number $\left(\sigma \left(N\right)\right)$ : $\sigma \left(N\right)=\left[\frac{P_1{}^{n_1+1}-1}{P_1-1}\right]\left[\frac{P_2{}^{n_2+1}-1}{P_2-1}\right]\mathrm{.......}\left[\frac{P_k{}^{n_k+1}-1}{P_k-1}\right]$

Product of divisors of $N=N^{\frac{1}{2}d\left(N\right)}$ .