21021073 has 4 divisors (see below), whose sum is σ = 21038308. Its totient is φ = 21003840.

The previous prime is 21021067. The next prime is 21021083. The reversal of 21021073 is 37012012.

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 18386944 + 2634129 = 4288^2 + 1623^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21021073 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21021043) 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, 6636 + ... + 9277.

It is an arithmetic number, because the mean of its divisors is an integer number (5259577).

Almost surely, 2^21021073 is an apocalyptic number.

It is an amenable number.

21021073 is a deficient number, since it is larger than the sum of its proper divisors (17235).

21021073 is a wasteful number, since it uses less digits than its factorization.

21021073 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17234.

The product of its (nonzero) digits is 84, while the sum is 16.

The square root of 21021073 is about 4584.8743712342. The cubic root of 21021073 is about 275.9846706112.

Adding to 21021073 its reverse (37012012), we get a palindrome (58033085).

The spelling of 21021073 in words is "twenty-one million, twenty-one thousand, seventy-three".