21005405943 has 8 divisors (see below), whose sum is σ = 28008479856. Its totient is φ = 14002968000.

The previous prime is 21005405903. The next prime is 21005405963. The reversal of 21005405943 is 34950450012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21005405943 - 2²¹ = 21003308791 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005405903) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 75688 + ... + 218493.

It is an arithmetic number, because the mean of its divisors is an integer number (3501059982).

Almost surely, 2^21005405943 is an apocalyptic number.

21005405943 is a deficient number, since it is larger than the sum of its proper divisors (7003073913).

21005405943 is a wasteful number, since it uses less digits than its factorization.

21005405943 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 317985.

The product of its (nonzero) digits is 21600, while the sum is 33.

Adding to 21005405943 its reverse (34950450012), we get a palindrome (55955855955).

The spelling of 21005405943 in words is "twenty-one billion, five million, four hundred five thousand, nine hundred forty-three".