21172001 has 4 divisors (see below), whose sum is σ = 21902100. Its totient is φ = 20441904.

The previous prime is 21171991. The next prime is 21172003. The reversal of 21172001 is 10027112.

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

It can be written as a sum of positive squares in 2 ways, for example, as 16613776 + 4558225 = 4076^2 + 2135^2 .

It is a cyclic number.

It is not a de Polignac number, because 21172001 - 2¹⁸ = 20909857 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21172003) 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, 365006 + ... + 365063.

It is an arithmetic number, because the mean of its divisors is an integer number (5475525).

Almost surely, 2^21172001 is an apocalyptic number.

It is an amenable number.

21172001 is a deficient number, since it is larger than the sum of its proper divisors (730099).

21172001 is an equidigital number, since it uses as much as digits as its factorization.

21172001 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 730098.

The product of its (nonzero) digits is 28, while the sum is 14.

The square root of 21172001 is about 4601.3042716169. The cubic root of 21172001 is about 276.6436049550.

Adding to 21172001 its reverse (10027112), we get a palindrome (31199113).

The spelling of 21172001 in words is "twenty-one million, one hundred seventy-two thousand, one".