21205641800 has 108 divisors (see below), whose sum is σ = 57391621065. Its totient is φ = 7265563200.

The previous prime is 21205641767. The next prime is 21205641827. The reversal of 21205641800 is 814650212.

It is a powerful number, because all its prime factors have an exponent greater than 1 and also an Achilles number because it is not a perfect power.

It can be written as a sum of positive squares in 2 ways, for example, as 20781528964 + 424112836 = 144158^2 + 20594^2 .

It is an ABA number since it can be written as A⋅B^A, here for A=2, B=102970.

It is an unprimeable number.

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 26 ways as a sum of consecutive naturals, for example, 14415065 + ... + 14416535.

Almost surely, 2^21205641800 is an apocalyptic number.

21205641800 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21205641800

21205641800 is an abundant number, since it is smaller than the sum of its proper divisors (36185979265).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21205641800 is an equidigital number, since it uses as much as digits as its factorization.

21205641800 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2972 (or 1485 counting only the distinct ones).

The product of its (nonzero) digits is 3840, while the sum is 29.

The spelling of 21205641800 in words is "twenty-one billion, two hundred five million, six hundred forty-one thousand, eight hundred".