21255591 has 8 divisors (see below), whose sum is σ = 32389504. Its totient is φ = 12146040.

The previous prime is 21255587. The next prime is 21255607. The reversal of 21255591 is 19555212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21255591 - 2² = 21255587 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21255541) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 506065 + ... + 506106.

It is an arithmetic number, because the mean of its divisors is an integer number (4048688).

Almost surely, 2^21255591 is an apocalyptic number.

21255591 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21255591 is a deficient number, since it is larger than the sum of its proper divisors (11133913).

21255591 is a wasteful number, since it uses less digits than its factorization.

21255591 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1012181.

The product of its digits is 4500, while the sum is 30.

The square root of 21255591 is about 4610.3786178578. The cubic root of 21255591 is about 277.0072026521.

The spelling of 21255591 in words is "twenty-one million, two hundred fifty-five thousand, five hundred ninety-one".