21340391 has 4 divisors (see below), whose sum is σ = 21551784. Its totient is φ = 21129000.

The previous prime is 21340387. The next prime is 21340409. The reversal of 21340391 is 19304312.

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 21340391 - 2² = 21340387 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21340351) 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, 105545 + ... + 105746.

It is an arithmetic number, because the mean of its divisors is an integer number (5387946).

Almost surely, 2^21340391 is an apocalyptic number.

21340391 is a deficient number, since it is larger than the sum of its proper divisors (211393).

21340391 is a wasteful number, since it uses less digits than its factorization.

21340391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 211392.

The product of its (nonzero) digits is 648, while the sum is 23.

The square root of 21340391 is about 4619.5661051662. The cubic root of 21340391 is about 277.3750908229.

It can be divided in two parts, 213 and 40391, that added together give a palindrome (40604).

The spelling of 21340391 in words is "twenty-one million, three hundred forty thousand, three hundred ninety-one".