21055751 has 4 divisors (see below), whose sum is σ = 21074904. Its totient is φ = 21036600.

The previous prime is 21055739. The next prime is 21055759. The reversal of 21055751 is 15755012.

It is a happy number.

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 21055751 - 2⁶ = 21055687 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21055751.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21055759) 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, 7820 + ... + 10161.

It is an arithmetic number, because the mean of its divisors is an integer number (5268726).

Almost surely, 2^21055751 is an apocalyptic number.

21055751 is a deficient number, since it is larger than the sum of its proper divisors (19153).

21055751 is a wasteful number, since it uses less digits than its factorization.

21055751 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19152.

The product of its (nonzero) digits is 1750, while the sum is 26.

The square root of 21055751 is about 4588.6545958483. The cubic root of 21055751 is about 276.1363491740.

The spelling of 21055751 in words is "twenty-one million, fifty-five thousand, seven hundred fifty-one".