21745931 has 4 divisors (see below), whose sum is σ = 21949272. Its totient is φ = 21542592.

The previous prime is 21745909. The next prime is 21745957. The reversal of 21745931 is 13954712.

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 21745931 - 2¹⁰ = 21744907 is a prime.

It is a super-2 number, since 2×21745931² = 945771030113522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21745901) 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, 101510 + ... + 101723.

It is an arithmetic number, because the mean of its divisors is an integer number (5487318).

Almost surely, 2^21745931 is an apocalyptic number.

21745931 is a deficient number, since it is larger than the sum of its proper divisors (203341).

21745931 is a wasteful number, since it uses less digits than its factorization.

21745931 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 203340.

The product of its digits is 7560, while the sum is 32.

The square root of 21745931 is about 4663.2532635490. The cubic root of 21745931 is about 279.1211003771.

The spelling of 21745931 in words is "twenty-one million, seven hundred forty-five thousand, nine hundred thirty-one".