20657721820 has 24 divisors (see below), whose sum is σ = 43505532000. Its totient is φ = 8239409472.

The previous prime is 20657721817. The next prime is 20657721827. The reversal of 20657721820 is 2812775602.

It is a happy number.

It is a super-2 number, since 2×20657721820² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20657721827) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1472800 + ... + 1486759.

It is an arithmetic number, because the mean of its divisors is an integer number (1812730500).

Almost surely, 2^20657721820 is an apocalyptic number.

20657721820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20657721820 is an abundant number, since it is smaller than the sum of its proper divisors (22847810180).

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

20657721820 is a wasteful number, since it uses less digits than its factorization.

20657721820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2959917 (or 2959915 counting only the distinct ones).

The product of its (nonzero) digits is 94080, while the sum is 40.

The spelling of 20657721820 in words is "twenty billion, six hundred fifty-seven million, seven hundred twenty-one thousand, eight hundred twenty".