21523381 has 8 divisors (see below), whose sum is σ = 24115104. Its totient is φ = 19037520.

The previous prime is 21523361. The next prime is 21523387. The reversal of 21523381 is 18332512.

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

It is a cyclic number.

It is not a de Polignac number, because 21523381 - 2¹¹ = 21521333 is a prime.

It is a super-2 number, since 2×21523381² = 926511859342322, which contains 22 as substring.

It is a Duffinian number.

It is a plaindrome in base 9.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21523387) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 26035 + ... + 26848.

It is an arithmetic number, because the mean of its divisors is an integer number (3014388).

Almost surely, 2^21523381 is an apocalyptic number.

It is an amenable number.

21523381 is a deficient number, since it is larger than the sum of its proper divisors (2591723).

21523381 is a wasteful number, since it uses less digits than its factorization.

21523381 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 52931.

The product of its digits is 1440, while the sum is 25.

The square root of 21523381 is about 4639.3298007363. The cubic root of 21523381 is about 278.1656492537.

Adding to 21523381 its reverse (18332512), we get a palindrome (39855893).

It can be divided in two parts, 21523 and 381, that added together give a square (21904 = 148²).

The spelling of 21523381 in words is "twenty-one million, five hundred twenty-three thousand, three hundred eighty-one".