21231251 has 4 divisors (see below), whose sum is σ = 21252504. Its totient is φ = 21210000.

The previous prime is 21231241. The next prime is 21231253. The reversal of 21231251 is 15213212.

It is a happy number.

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 21231251 - 2¹⁰ = 21230227 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21231253) 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, 9050 + ... + 11151.

It is an arithmetic number, because the mean of its divisors is an integer number (5313126).

Almost surely, 2^21231251 is an apocalyptic number.

21231251 is a deficient number, since it is larger than the sum of its proper divisors (21253).

21231251 is a wasteful number, since it uses less digits than its factorization.

21231251 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21252.

The product of its digits is 120, while the sum is 17.

The square root of 21231251 is about 4607.7381653041. The cubic root of 21231251 is about 276.9014276503.

Adding to 21231251 its reverse (15213212), we get a palindrome (36444463).

The spelling of 21231251 in words is "twenty-one million, two hundred thirty-one thousand, two hundred fifty-one".