21312197 has 4 divisors (see below), whose sum is σ = 21765696. Its totient is φ = 20858700.

The previous prime is 21312173. The next prime is 21312223. The reversal of 21312197 is 79121312.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21312197 - 2¹⁸ = 21050053 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 (21312107) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 226679 + ... + 226772.

It is an arithmetic number, because the mean of its divisors is an integer number (5441424).

Almost surely, 2^21312197 is an apocalyptic number.

It is an amenable number.

21312197 is a deficient number, since it is larger than the sum of its proper divisors (453499).

21312197 is an equidigital number, since it uses as much as digits as its factorization.

21312197 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 453498.

The product of its digits is 756, while the sum is 26.

The square root of 21312197 is about 4616.5135112983. The cubic root of 21312197 is about 277.2528850052.

The spelling of 21312197 in words is "twenty-one million, three hundred twelve thousand, one hundred ninety-seven".