20621021 has 4 divisors (see below), whose sum is σ = 20630844. Its totient is φ = 20611200.

The previous prime is 20621009. The next prime is 20621063. The reversal of 20621021 is 12012602.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 15912121 + 4708900 = 3989^2 + 2170^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20621021 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 20620987 and 20621005.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20621071) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 350 + ... + 6431.

It is an arithmetic number, because the mean of its divisors is an integer number (5157711).

Almost surely, 2^20621021 is an apocalyptic number.

It is an amenable number.

20621021 is a deficient number, since it is larger than the sum of its proper divisors (9823).

20621021 is an equidigital number, since it uses as much as digits as its factorization.

20621021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9822.

The product of its (nonzero) digits is 48, while the sum is 14.

The square root of 20621021 is about 4541.0374365336. The cubic root of 20621021 is about 274.2226908953. Note that the first 3 decimals are identical.

Adding to 20621021 its reverse (12012602), we get a palindrome (32633623).

The spelling of 20621021 in words is "twenty million, six hundred twenty-one thousand, twenty-one".