21255551 has 8 divisors (see below), whose sum is σ = 21583200. Its totient is φ = 20930400.

The previous prime is 21255541. The next prime is 21255557. The reversal of 21255551 is 15555212.

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

It is a cyclic number.

It is not a de Polignac number, because 21255551 - 2¹⁸ = 20993407 is a prime.

It is a Duffinian number.

It is a plaindrome in base 16.

It is a self number, because there is not a number n which added to its sum of digits gives 21255551.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21255557) 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, 22670 + ... + 23588.

It is an arithmetic number, because the mean of its divisors is an integer number (2697900).

Almost surely, 2^21255551 is an apocalyptic number.

21255551 is a deficient number, since it is larger than the sum of its proper divisors (327649).

21255551 is a wasteful number, since it uses less digits than its factorization.

21255551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1249.

The product of its digits is 2500, while the sum is 26.

The square root of 21255551 is about 4610.3742798172. The cubic root of 21255551 is about 277.0070288893.

The spelling of 21255551 in words is "twenty-one million, two hundred fifty-five thousand, five hundred fifty-one".