21310391 has 4 divisors (see below), whose sum is σ = 21517392. Its totient is φ = 21103392.

The previous prime is 21310337. The next prime is 21310417. The reversal of 21310391 is 19301312.

21310391 = 93² + 94² + ... + 401².

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 21310391 - 2²² = 17116087 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 (21310301) 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, 103346 + ... + 103551.

It is an arithmetic number, because the mean of its divisors is an integer number (5379348).

Almost surely, 2^21310391 is an apocalyptic number.

21310391 is a deficient number, since it is larger than the sum of its proper divisors (207001).

21310391 is a wasteful number, since it uses less digits than its factorization.

21310391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 207000.

The product of its (nonzero) digits is 162, while the sum is 20.

The square root of 21310391 is about 4616.3179049974. The cubic root of 21310391 is about 277.2450532950.

The spelling of 21310391 in words is "twenty-one million, three hundred ten thousand, three hundred ninety-one".