21812543 has 4 divisors (see below), whose sum is σ = 21841968. Its totient is φ = 21783120.

The previous prime is 21812537. The next prime is 21812591. The reversal of 21812543 is 34521812.

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

It is a cyclic number.

It is not a de Polignac number, because 21812543 - 2¹⁶ = 21747007 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21812143) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 13571 + ... + 15092.

It is an arithmetic number, because the mean of its divisors is an integer number (5460492).

Almost surely, 2^21812543 is an apocalyptic number.

21812543 is a deficient number, since it is larger than the sum of its proper divisors (29425).

21812543 is an equidigital number, since it uses as much as digits as its factorization.

21812543 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 29424.

The product of its digits is 1920, while the sum is 26.

The square root of 21812543 is about 4670.3900265395. The cubic root of 21812543 is about 279.4058105376.

The spelling of 21812543 in words is "twenty-one million, eight hundred twelve thousand, five hundred forty-three".