20970821 has 2 divisors, whose sum is σ = 20970822. Its totient is φ = 20970820.

The previous prime is 20970811. The next prime is 20970827. The reversal of 20970821 is 12807902.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20802721 + 168100 = 4561^2 + 410^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20970821 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20970827) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10485410 + 10485411.

It is an arithmetic number, because the mean of its divisors is an integer number (10485411).

Almost surely, 2^20970821 is an apocalyptic number.

It is an amenable number.

20970821 is a deficient number, since it is larger than the sum of its proper divisors (1).

20970821 is an equidigital number, since it uses as much as digits as its factorization.

20970821 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2016, while the sum is 29.

The square root of 20970821 is about 4579.3908983619. The cubic root of 20970821 is about 275.7645764272.

The spelling of 20970821 in words is "twenty million, nine hundred seventy thousand, eight hundred twenty-one".