21311399 has 2 divisors, whose sum is σ = 21311400. Its totient is φ = 21311398.

The previous prime is 21311393. The next prime is 21311413. The reversal of 21311399 is 99311312.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21311399 - 2²⁴ = 4534183 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21311393) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10655699 + 10655700.

It is an arithmetic number, because the mean of its divisors is an integer number (10655700).

Almost surely, 2^21311399 is an apocalyptic number.

21311399 is a deficient number, since it is larger than the sum of its proper divisors (1).

21311399 is an equidigital number, since it uses as much as digits as its factorization.

21311399 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1458, while the sum is 29.

The square root of 21311399 is about 4616.4270816293. The cubic root of 21311399 is about 277.2494245366.

The spelling of 21311399 in words is "twenty-one million, three hundred eleven thousand, three hundred ninety-nine".