21717887 has 4 divisors (see below), whose sum is σ = 22418496. Its totient is φ = 21017280.

The previous prime is 21717827. The next prime is 21717907. The reversal of 21717887 is 78871712.

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 21717887 - 2¹⁸ = 21455743 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 (21717827) 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, 350258 + ... + 350319.

It is an arithmetic number, because the mean of its divisors is an integer number (5604624).

Almost surely, 2^21717887 is an apocalyptic number.

21717887 is a deficient number, since it is larger than the sum of its proper divisors (700609).

21717887 is an equidigital number, since it uses as much as digits as its factorization.

21717887 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 700608.

The product of its digits is 43904, while the sum is 41.

The square root of 21717887 is about 4660.2453798057. The cubic root of 21717887 is about 279.0010619899.

The spelling of 21717887 in words is "twenty-one million, seven hundred seventeen thousand, eight hundred eighty-seven".