21813538 has 4 divisors (see below), whose sum is σ = 32720310. Its totient is φ = 10906768.

The previous prime is 21813527. The next prime is 21813563. The reversal of 21813538 is 83531812.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 13010449 + 8803089 = 3607^2 + 2967^2 .

It is an unprimeable number.

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 as a sum of consecutive naturals, namely, 5453383 + ... + 5453386.

Almost surely, 2^21813538 is an apocalyptic number.

21813538 is a deficient number, since it is larger than the sum of its proper divisors (10906772).

21813538 is a wasteful number, since it uses less digits than its factorization.

21813538 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10906771.

The product of its digits is 5760, while the sum is 31.

The square root of 21813538 is about 4670.4965474776. The cubic root of 21813538 is about 279.4100589274.

The spelling of 21813538 in words is "twenty-one million, eight hundred thirteen thousand, five hundred thirty-eight".