21045751 has 4 divisors (see below), whose sum is σ = 21559104. Its totient is φ = 20532400.

The previous prime is 21045737. The next prime is 21045757. The reversal of 21045751 is 15754012.

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

It is a cyclic number.

It is not a de Polignac number, because 21045751 - 2⁵ = 21045719 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21045757) 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, 256615 + ... + 256696.

It is an arithmetic number, because the mean of its divisors is an integer number (5389776).

Almost surely, 2^21045751 is an apocalyptic number.

21045751 is a deficient number, since it is larger than the sum of its proper divisors (513353).

21045751 is an equidigital number, since it uses as much as digits as its factorization.

21045751 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 513352.

The product of its (nonzero) digits is 1400, while the sum is 25.

The square root of 21045751 is about 4587.5648224303. The cubic root of 21045751 is about 276.0926271404.

Adding to 21045751 its reverse (15754012), we get a palindrome (36799763).

The spelling of 21045751 in words is "twenty-one million, forty-five thousand, seven hundred fifty-one".