21052491 has 4 divisors (see below), whose sum is σ = 28069992. Its totient is φ = 14034992.

The previous prime is 21052489. The next prime is 21052547. The reversal of 21052491 is 19425012.

Added to its reverse (19425012) it gives a triangular number (40477503 = T₈₉₉₇).

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 21052491 - 2¹ = 21052489 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21052411) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3508746 + ... + 3508751.

It is an arithmetic number, because the mean of its divisors is an integer number (7017498).

Almost surely, 2^21052491 is an apocalyptic number.

21052491 is a deficient number, since it is larger than the sum of its proper divisors (7017501).

21052491 is an equidigital number, since it uses as much as digits as its factorization.

21052491 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7017500.

The product of its (nonzero) digits is 720, while the sum is 24.

The square root of 21052491 is about 4588.2993581500. The cubic root of 21052491 is about 276.1220973122.

Adding to 21052491 its reverse (19425012), we get a triangular number (40477503 = T₈₉₉₇).

The spelling of 21052491 in words is "twenty-one million, fifty-two thousand, four hundred ninety-one".