21813481 has 4 divisors (see below), whose sum is σ = 22565700. Its totient is φ = 21061264.

The previous prime is 21813469. The next prime is 21813487. The reversal of 21813481 is 18431812.

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

It can be written as a sum of positive squares in 2 ways, for example, as 4665600 + 17147881 = 2160^2 + 4141^2 .

It is a cyclic number.

It is not a de Polignac number, because 21813481 - 2¹⁵ = 21780713 is a prime.

It is a super-2 number, since 2×21813481² = 951655906674722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21813487) 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 3 ways as a sum of consecutive naturals, for example, 376066 + ... + 376123.

It is an arithmetic number, because the mean of its divisors is an integer number (5641425).

Almost surely, 2^21813481 is an apocalyptic number.

It is an amenable number.

21813481 is a deficient number, since it is larger than the sum of its proper divisors (752219).

21813481 is an equidigital number, since it uses as much as digits as its factorization.

21813481 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 752218.

The product of its digits is 1536, while the sum is 28.

The square root of 21813481 is about 4670.4904453387. The cubic root of 21813481 is about 279.4098155558.

The spelling of 21813481 in words is "twenty-one million, eight hundred thirteen thousand, four hundred eighty-one".