21252991 has 4 divisors (see below), whose sum is σ = 21472192. Its totient is φ = 21033792.

The previous prime is 21252983. The next prime is 21252997. The reversal of 21252991 is 19925212.

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 21252991 - 2³ = 21252983 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 (21252997) 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, 109455 + ... + 109648.

It is an arithmetic number, because the mean of its divisors is an integer number (5368048).

Almost surely, 2^21252991 is an apocalyptic number.

21252991 is a deficient number, since it is larger than the sum of its proper divisors (219201).

21252991 is an equidigital number, since it uses as much as digits as its factorization.

21252991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 219200.

The product of its digits is 3240, while the sum is 31.

The square root of 21252991 is about 4610.0966367312. The cubic root of 21252991 is about 276.9959076146.

The spelling of 21252991 in words is "twenty-one million, two hundred fifty-two thousand, nine hundred ninety-one".