21201691 has 4 divisors (see below), whose sum is σ = 24230512. Its totient is φ = 18172872.

The previous prime is 21201689. The next prime is 21201707. The reversal of 21201691 is 19610212.

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 21201691 - 2¹ = 21201689 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21201611) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1514400 + ... + 1514413.

It is an arithmetic number, because the mean of its divisors is an integer number (6057628).

Almost surely, 2^21201691 is an apocalyptic number.

21201691 is a deficient number, since it is larger than the sum of its proper divisors (3028821).

21201691 is an equidigital number, since it uses as much as digits as its factorization.

21201691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3028820.

The product of its (nonzero) digits is 216, while the sum is 22.

The square root of 21201691 is about 4604.5294004925. The cubic root of 21201691 is about 276.7728591883.

The spelling of 21201691 in words is "twenty-one million, two hundred one thousand, six hundred ninety-one".