21720255156 has 72 divisors (see below), whose sum is σ = 61193321280. Its totient is φ = 6455552256.

The previous prime is 21720255133. The next prime is 21720255187. The reversal of 21720255156 is 65155202712.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a self number, because there is not a number n which added to its sum of digits gives 21720255156.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 922336 + ... + 945591.

It is an arithmetic number, because the mean of its divisors is an integer number (849907240).

Almost surely, 2^21720255156 is an apocalyptic number.

It is an amenable number.

21720255156 is an abundant number, since it is smaller than the sum of its proper divisors (39473066124).

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

21720255156 is a wasteful number, since it uses less digits than its factorization.

21720255156 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1867973 (or 1867968 counting only the distinct ones).

The product of its (nonzero) digits is 42000, while the sum is 36.

Adding to 21720255156 its reverse (65155202712), we get a palindrome (86875457868).

The spelling of 21720255156 in words is "twenty-one billion, seven hundred twenty million, two hundred fifty-five thousand, one hundred fifty-six".