21381537 has 16 divisors (see below), whose sum is σ = 29918720. Its totient is φ = 13564800.

The previous prime is 21381527. The next prime is 21381539. The reversal of 21381537 is 73518312.

It is not a de Polignac number, because 21381537 - 2⁸ = 21381281 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21381539) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3789 + ... + 7557.

It is an arithmetic number, because the mean of its divisors is an integer number (1869920).

Almost surely, 2^21381537 is an apocalyptic number.

It is an amenable number.

21381537 is a deficient number, since it is larger than the sum of its proper divisors (8537183).

21381537 is a wasteful number, since it uses less digits than its factorization.

21381537 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3864.

The product of its digits is 5040, while the sum is 30.

The square root of 21381537 is about 4624.0174091368. The cubic root of 21381537 is about 277.5532435779.

Adding to 21381537 its reverse (73518312), we get a palindrome (94899849).

The spelling of 21381537 in words is "twenty-one million, three hundred eighty-one thousand, five hundred thirty-seven".