21617391 has 4 divisors (see below), whose sum is σ = 28823192. Its totient is φ = 14411592.

The previous prime is 21617381. The next prime is 21617411. The reversal of 21617391 is 19371612.

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

It is not a de Polignac number, because 21617391 - 2¹⁹ = 21093103 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 (21617341) 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, 3602896 + ... + 3602901.

It is an arithmetic number, because the mean of its divisors is an integer number (7205798).

Almost surely, 2^21617391 is an apocalyptic number.

21617391 is a deficient number, since it is larger than the sum of its proper divisors (7205801).

21617391 is an equidigital number, since it uses as much as digits as its factorization.

21617391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7205800.

The product of its digits is 2268, while the sum is 30.

The square root of 21617391 is about 4649.4506127068. The cubic root of 21617391 is about 278.5700524399.

The spelling of 21617391 in words is "twenty-one million, six hundred seventeen thousand, three hundred ninety-one".