21380537 has 4 divisors (see below), whose sum is σ = 21412980. Its totient is φ = 21348096.

The previous prime is 21380521. The next prime is 21380539. The reversal of 21380537 is 73508312.

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 6295081 + 15085456 = 2509^2 + 3884^2 .

It is a cyclic number.

It is not a de Polignac number, because 21380537 - 2⁴ = 21380521 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21380539) 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, 15212 + ... + 16557.

It is an arithmetic number, because the mean of its divisors is an integer number (5353245).

Almost surely, 2^21380537 is an apocalyptic number.

It is an amenable number.

21380537 is a deficient number, since it is larger than the sum of its proper divisors (32443).

21380537 is an equidigital number, since it uses as much as digits as its factorization.

21380537 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 32442.

The product of its (nonzero) digits is 5040, while the sum is 29.

The square root of 21380537 is about 4623.9092767917. The cubic root of 21380537 is about 277.5489165181.

Adding to 21380537 its reverse (73508312), we get a palindrome (94888849).

The spelling of 21380537 in words is "twenty-one million, three hundred eighty thousand, five hundred thirty-seven".