20805643 has 2 divisors, whose sum is σ = 20805644. Its totient is φ = 20805642.

The previous prime is 20805623. The next prime is 20805647. The reversal of 20805643 is 34650802.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 20805643 - 2⁵ = 20805611 is a prime.

It is not a weakly prime, because it can be changed into another prime (20805647) 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 as a sum of consecutive naturals, namely, 10402821 + 10402822.

It is an arithmetic number, because the mean of its divisors is an integer number (10402822).

Almost surely, 2^20805643 is an apocalyptic number.

20805643 is a deficient number, since it is larger than the sum of its proper divisors (1).

20805643 is an equidigital number, since it uses as much as digits as its factorization.

20805643 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5760, while the sum is 28.

The square root of 20805643 is about 4561.3203132426. The cubic root of 20805643 is about 275.0386414020.

The spelling of 20805643 in words is "twenty million, eight hundred five thousand, six hundred forty-three".