21418391 has 4 divisors (see below), whose sum is σ = 21615000. Its totient is φ = 21221784.

The previous prime is 21418379. The next prime is 21418403. The reversal of 21418391 is 19381412.

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

It is an interprime number because it is at equal distance from previous prime (21418379) and next prime (21418403).

It is a cyclic number.

It is not a de Polignac number, because 21418391 - 2²² = 17224087 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 (21414391) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 98141 + ... + 98358.

It is an arithmetic number, because the mean of its divisors is an integer number (5403750).

Almost surely, 2^21418391 is an apocalyptic number.

21418391 is a deficient number, since it is larger than the sum of its proper divisors (196609).

21418391 is a wasteful number, since it uses less digits than its factorization.

21418391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 196608.

The product of its digits is 1728, while the sum is 29.

The square root of 21418391 is about 4628.0007562661. Note that the first 3 decimals coincide. The cubic root of 21418391 is about 277.7126190220.

The spelling of 21418391 in words is "twenty-one million, four hundred eighteen thousand, three hundred ninety-one".