21372005 has 4 divisors (see below), whose sum is σ = 25646412. Its totient is φ = 17097600.

The previous prime is 21371993. The next prime is 21372007. The reversal of 21372005 is 50027312.

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 12124324 + 9247681 = 3482^2 + 3041^2 .

It is not a de Polignac number, because 21372005 - 2¹⁰ = 21370981 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21372007) 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, 2137196 + ... + 2137205.

It is an arithmetic number, because the mean of its divisors is an integer number (6411603).

Almost surely, 2^21372005 is an apocalyptic number.

It is an amenable number.

21372005 is a deficient number, since it is larger than the sum of its proper divisors (4274407).

21372005 is an equidigital number, since it uses as much as digits as its factorization.

21372005 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4274406.

The product of its (nonzero) digits is 420, while the sum is 20.

The square root of 21372005 is about 4622.9865887757. The cubic root of 21372005 is about 277.5119925559.

Adding to 21372005 its reverse (50027312), we get a palindrome (71399317).

The spelling of 21372005 in words is "twenty-one million, three hundred seventy-two thousand, five".