21745487 has 4 divisors (see below), whose sum is σ = 22251240. Its totient is φ = 21239736.

The previous prime is 21745483. The next prime is 21745517. The reversal of 21745487 is 78454712.

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 21745487 - 2² = 21745483 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 21745487.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21745483) 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, 252812 + ... + 252897.

It is an arithmetic number, because the mean of its divisors is an integer number (5562810).

Almost surely, 2^21745487 is an apocalyptic number.

21745487 is a deficient number, since it is larger than the sum of its proper divisors (505753).

21745487 is an equidigital number, since it uses as much as digits as its factorization.

21745487 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 505752.

The product of its digits is 62720, while the sum is 38.

The square root of 21745487 is about 4663.2056570561. The cubic root of 21745487 is about 279.1192007020.

The spelling of 21745487 in words is "twenty-one million, seven hundred forty-five thousand, four hundred eighty-seven".