21005309443 has 2 divisors, whose sum is σ = 21005309444. Its totient is φ = 21005309442.

The previous prime is 21005309407. The next prime is 21005309453. The reversal of 21005309443 is 34490350012.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21005309443 - 2¹⁷ = 21005178371 is a prime.

It is not a weakly prime, because it can be changed into another prime (21005309453) 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, 10502654721 + 10502654722.

It is an arithmetic number, because the mean of its divisors is an integer number (10502654722).

Almost surely, 2^21005309443 is an apocalyptic number.

21005309443 is a deficient number, since it is larger than the sum of its proper divisors (1).

21005309443 is an equidigital number, since it uses as much as digits as its factorization.

21005309443 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 12960, while the sum is 31.

Adding to 21005309443 its reverse (34490350012), we get a palindrome (55495659455).

The spelling of 21005309443 in words is "twenty-one billion, five million, three hundred nine thousand, four hundred forty-three".