21720864400 has 45 divisors (see below), whose sum is σ = 52191459291. Its totient is φ = 8687166720.

The previous prime is 21720864371. The next prime is 21720864401. The reversal of 21720864400 is 446802712.

It is a happy number.

The square root of 21720864400 is 147380.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in 4 ways, for example, as 2738638224 + 18982226176 = 52332^2 + 137776^2 .

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21720864401) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 2943916 + ... + 2951284.

Almost surely, 2^21720864400 is an apocalyptic number.

21720864400 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

21720864400 is the 147380-th square number.

It is an amenable number.

21720864400 is an abundant number, since it is smaller than the sum of its proper divisors (30470594891).

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

21720864400 is an frugal number, since it uses more digits than its factorization.

21720864400 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14756 (or 7376 counting only the distinct ones).

The product of its (nonzero) digits is 21504, while the sum is 34.

The spelling of 21720864400 in words is "twenty-one billion, seven hundred twenty million, eight hundred sixty-four thousand, four hundred".