21231551 has 8 divisors (see below), whose sum is σ = 23700864. Its totient is φ = 18852120.

The previous prime is 21231547. The next prime is 21231557. The reversal of 21231551 is 15513212.

It is a happy number.

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 21231551 - 2² = 21231547 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21231557) 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, 21971 + ... + 22916.

It is an arithmetic number, because the mean of its divisors is an integer number (2962608).

Almost surely, 2^21231551 is an apocalyptic number.

21231551 is a deficient number, since it is larger than the sum of its proper divisors (2469313).

21231551 is a wasteful number, since it uses less digits than its factorization.

21231551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 44941.

The product of its digits is 300, while the sum is 20.

The square root of 21231551 is about 4607.7707191222. The cubic root of 21231551 is about 276.9027318604.

Adding to 21231551 its reverse (15513212), we get a palindrome (36744763).

The spelling of 21231551 in words is "twenty-one million, two hundred thirty-one thousand, five hundred fifty-one".