20555721 has 32 divisors (see below), whose sum is σ = 32256000. Its totient is φ = 12911184.

The previous prime is 20555699. The next prime is 20555747. The reversal of 20555721 is 12755502.

It is a happy number.

It is not a de Polignac number, because 20555721 - 2⁹ = 20555209 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (20555791) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 48850 + ... + 49268.

It is an arithmetic number, because the mean of its divisors is an integer number (1008000).

Almost surely, 2^20555721 is an apocalyptic number.

It is an amenable number.

20555721 is a deficient number, since it is larger than the sum of its proper divisors (11700279).

20555721 is a wasteful number, since it uses less digits than its factorization.

20555721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 530 (or 524 counting only the distinct ones).

The product of its (nonzero) digits is 3500, while the sum is 27.

The square root of 20555721 is about 4533.8417484513. The cubic root of 20555721 is about 273.9329270886.

It can be divided in two parts, 2055 and 5721, that added together give a 5-th power (7776 = 6⁵).

The spelling of 20555721 in words is "twenty million, five hundred fifty-five thousand, seven hundred twenty-one".