21351381 has 8 divisors (see below), whose sum is σ = 28496160. Its totient is φ = 14220432.

The previous prime is 21351361. The next prime is 21351389. The reversal of 21351381 is 18315312.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21351381 - 2⁹ = 21350869 is a prime.

It is a super-2 number, since 2×21351381² = 911762941214322, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21351389) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 951 + ... + 6603.

It is an arithmetic number, because the mean of its divisors is an integer number (3562020).

Almost surely, 2^21351381 is an apocalyptic number.

It is an amenable number.

21351381 is a deficient number, since it is larger than the sum of its proper divisors (7144779).

21351381 is a wasteful number, since it uses less digits than its factorization.

21351381 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6915.

The product of its digits is 720, while the sum is 24.

The square root of 21351381 is about 4620.7554577147. The cubic root of 21351381 is about 277.4226974031.

Adding to 21351381 its reverse (18315312), we get a palindrome (39666693).

The spelling of 21351381 in words is "twenty-one million, three hundred fifty-one thousand, three hundred eighty-one".