21640191 has 4 divisors (see below), whose sum is σ = 28853592. Its totient is φ = 14426792.

The previous prime is 21640189. The next prime is 21640219. The reversal of 21640191 is 19104612.

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 21640191 - 2¹ = 21640189 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21640121) 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, 3606696 + ... + 3606701.

It is an arithmetic number, because the mean of its divisors is an integer number (7213398).

Almost surely, 2^21640191 is an apocalyptic number.

21640191 is a deficient number, since it is larger than the sum of its proper divisors (7213401).

21640191 is an equidigital number, since it uses as much as digits as its factorization.

21640191 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7213400.

The product of its (nonzero) digits is 432, while the sum is 24.

The square root of 21640191 is about 4651.9018691284. The cubic root of 21640191 is about 278.6679545649.

The spelling of 21640191 in words is "twenty-one million, six hundred forty thousand, one hundred ninety-one".