21289391 has 4 divisors (see below), whose sum is σ = 21457152. Its totient is φ = 21121632.

The previous prime is 21289381. The next prime is 21289399. The reversal of 21289391 is 19398212.

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-21289391 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 (21289399) 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, 83690 + ... + 83943.

It is an arithmetic number, because the mean of its divisors is an integer number (5364288).

Almost surely, 2^21289391 is an apocalyptic number.

21289391 is a deficient number, since it is larger than the sum of its proper divisors (167761).

21289391 is a wasteful number, since it uses less digits than its factorization.

21289391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 167760.

The product of its digits is 7776, while the sum is 35.

The square root of 21289391 is about 4614.0428043095. The cubic root of 21289391 is about 277.1539543937.

The spelling of 21289391 in words is "twenty-one million, two hundred eighty-nine thousand, three hundred ninety-one".