21224551 has 4 divisors (see below), whose sum is σ = 22473072. Its totient is φ = 19976032.

The previous prime is 21224521. The next prime is 21224557. The reversal of 21224551 is 15542212.

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 21224551 - 2¹¹ = 21222503 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 (21224557) 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, 624235 + ... + 624268.

It is an arithmetic number, because the mean of its divisors is an integer number (5618268).

Almost surely, 2^21224551 is an apocalyptic number.

21224551 is a deficient number, since it is larger than the sum of its proper divisors (1248521).

21224551 is a wasteful number, since it uses less digits than its factorization.

21224551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1248520.

The product of its digits is 800, while the sum is 22.

The square root of 21224551 is about 4607.0110700974. The cubic root of 21224551 is about 276.8722970894.

Adding to 21224551 its reverse (15542212), we get a palindrome (36766763).

The spelling of 21224551 in words is "twenty-one million, two hundred twenty-four thousand, five hundred fifty-one".