21866591 has 4 divisors (see below), whose sum is σ = 22078992. Its totient is φ = 21654192.

The previous prime is 21866567. The next prime is 21866597. The reversal of 21866591 is 19566812.

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 21866591 - 2⁶ = 21866527 is a prime.

It is a super-2 number, since 2×21866591² = 956295603922562, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21866597) 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, 106046 + ... + 106251.

It is an arithmetic number, because the mean of its divisors is an integer number (5519748).

Almost surely, 2^21866591 is an apocalyptic number.

21866591 is a deficient number, since it is larger than the sum of its proper divisors (212401).

21866591 is a wasteful number, since it uses less digits than its factorization.

21866591 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 212400.

The product of its digits is 25920, while the sum is 38.

The square root of 21866591 is about 4676.1726871449. The cubic root of 21866591 is about 279.6363945262.

The spelling of 21866591 in words is "twenty-one million, eight hundred sixty-six thousand, five hundred ninety-one".