20721245 has 4 divisors (see below), whose sum is σ = 24865500. Its totient is φ = 16576992.

The previous prime is 20721223. The next prime is 20721263. The reversal of 20721245 is 54212702.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 11546404 + 9174841 = 3398^2 + 3029^2 .

It is a cyclic number.

It is not a de Polignac number, because 20721245 - 2¹⁰ = 20720221 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 20721245.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2072120 + ... + 2072129.

It is an arithmetic number, because the mean of its divisors is an integer number (6216375).

Almost surely, 2^20721245 is an apocalyptic number.

It is an amenable number.

20721245 is a deficient number, since it is larger than the sum of its proper divisors (4144255).

20721245 is an equidigital number, since it uses as much as digits as its factorization.

20721245 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4144254.

The product of its (nonzero) digits is 1120, while the sum is 23.

The square root of 20721245 is about 4552.0594240409. The cubic root of 20721245 is about 274.6662397159. Note that the first 3 decimals are identical.

Adding to 20721245 its reverse (54212702), we get a palindrome (74933947).

The spelling of 20721245 in words is "twenty million, seven hundred twenty-one thousand, two hundred forty-five".