21730751 has 4 divisors (see below), whose sum is σ = 24835152. Its totient is φ = 18626352.

The previous prime is 21730747. The next prime is 21730759. The reversal of 21730751 is 15703712.

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 21730751 - 2² = 21730747 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 21730751.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21730759) 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, 1552190 + ... + 1552203.

It is an arithmetic number, because the mean of its divisors is an integer number (6208788).

Almost surely, 2^21730751 is an apocalyptic number.

21730751 is a deficient number, since it is larger than the sum of its proper divisors (3104401).

21730751 is an equidigital number, since it uses as much as digits as its factorization.

21730751 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3104400.

The product of its (nonzero) digits is 1470, while the sum is 26.

The square root of 21730751 is about 4661.6253603223. The cubic root of 21730751 is about 279.0561373488.

The spelling of 21730751 in words is "twenty-one million, seven hundred thirty thousand, seven hundred fifty-one".