21644543 has 2 divisors, whose sum is σ = 21644544. Its totient is φ = 21644542.

The previous prime is 21644531. The next prime is 21644611. The reversal of 21644543 is 34544612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21644543 - 2¹⁰ = 21643519 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21646543) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10822271 + 10822272.

It is an arithmetic number, because the mean of its divisors is an integer number (10822272).

Almost surely, 2^21644543 is an apocalyptic number.

21644543 is a deficient number, since it is larger than the sum of its proper divisors (1).

21644543 is an equidigital number, since it uses as much as digits as its factorization.

21644543 is an evil number, because the sum of its binary digits is even.

The product of its digits is 11520, while the sum is 29.

The square root of 21644543 is about 4652.3696112841. The cubic root of 21644543 is about 278.6866340311.

The spelling of 21644543 in words is "twenty-one million, six hundred forty-four thousand, five hundred forty-three".