21142391 has 4 divisors (see below), whose sum is σ = 21154800. Its totient is φ = 21129984.

The previous prime is 21142379. The next prime is 21142393. The reversal of 21142391 is 19324112.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21142391 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 (21142393) 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, 3146 + ... + 7223.

It is an arithmetic number, because the mean of its divisors is an integer number (5288700).

Almost surely, 2^21142391 is an apocalyptic number.

21142391 is a deficient number, since it is larger than the sum of its proper divisors (12409).

21142391 is a wasteful number, since it uses less digits than its factorization.

21142391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12408.

The product of its digits is 432, while the sum is 23.

The square root of 21142391 is about 4598.0855798908. The cubic root of 21142391 is about 276.5145785930.

The spelling of 21142391 in words is "twenty-one million, one hundred forty-two thousand, three hundred ninety-one".