21312251 has 8 divisors (see below), whose sum is σ = 22009344. Its totient is φ = 20623680.

The previous prime is 21312233. The next prime is 21312257. The reversal of 21312251 is 15221312.

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 a de Polignac number, because none of the positive numbers 2^k-21312251 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21312257) 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, 3161 + ... + 7253.

It is an arithmetic number, because the mean of its divisors is an integer number (2751168).

Almost surely, 2^21312251 is an apocalyptic number.

21312251 is a deficient number, since it is larger than the sum of its proper divisors (697093).

21312251 is a wasteful number, since it uses less digits than its factorization.

21312251 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4261.

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

The square root of 21312251 is about 4616.5193598641. The cubic root of 21312251 is about 277.2531191691.

Adding to 21312251 its reverse (15221312), we get a palindrome (36533563).

The spelling of 21312251 in words is "twenty-one million, three hundred twelve thousand, two hundred fifty-one".