21535381 has 4 divisors (see below), whose sum is σ = 24611872. Its totient is φ = 18458892.

The previous prime is 21535363. The next prime is 21535391. The reversal of 21535381 is 18353512.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21535381 - 2⁷ = 21535253 is a prime.

It is a super-2 number, since 2×21535381² = 927545269630322, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21535351) 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, 1538235 + ... + 1538248.

It is an arithmetic number, because the mean of its divisors is an integer number (6152968).

Almost surely, 2^21535381 is an apocalyptic number.

It is an amenable number.

21535381 is a deficient number, since it is larger than the sum of its proper divisors (3076491).

21535381 is an equidigital number, since it uses as much as digits as its factorization.

21535381 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3076490.

The product of its digits is 3600, while the sum is 28.

The square root of 21535381 is about 4640.6229107739. The cubic root of 21535381 is about 278.2173351797.

Adding to 21535381 its reverse (18353512), we get a palindrome (39888893).

The spelling of 21535381 in words is "twenty-one million, five hundred thirty-five thousand, three hundred eighty-one".