21805397641 has 16 divisors (see below), whose sum is σ = 23399570304. Its totient is φ = 20272430464.

The previous prime is 21805397639. The next prime is 21805397659. The reversal of 21805397641 is 14679350812.

It is not a de Polignac number, because 21805397641 - 2¹ = 21805397639 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21805397591 and 21805397600.

It is not an unprimeable number, because it can be changed into a prime (21805397611) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 46845 + ... + 214021.

It is an arithmetic number, because the mean of its divisors is an integer number (1462473144).

It is a 2-persistent number, because it is pandigital, and so is 2⋅21805397641 = 43610795282, but 3⋅21805397641 = 65416192923 is not.

Almost surely, 2^21805397641 is an apocalyptic number.

21805397641 is the 93393-rd centered pentagonal number.

It is an amenable number.

21805397641 is a deficient number, since it is larger than the sum of its proper divisors (1594172663).

21805397641 is a wasteful number, since it uses less digits than its factorization.

21805397641 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 167360.

The product of its (nonzero) digits is 362880, while the sum is 46.

The spelling of 21805397641 in words is "twenty-one billion, eight hundred five million, three hundred ninety-seven thousand, six hundred forty-one".