20721855 has 72 divisors (see below), whose sum is σ = 42574896. Its totient is φ = 8574720.

The previous prime is 20721817. The next prime is 20721871. The reversal of 20721855 is 55812702.

It is not a de Polignac number, because 20721855 - 2⁶ = 20721791 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 88819 + ... + 89051.

It is an arithmetic number, because the mean of its divisors is an integer number (591318).

Almost surely, 2^20721855 is an apocalyptic number.

20721855 is an abundant number, since it is smaller than the sum of its proper divisors (21853041).

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

20721855 is a wasteful number, since it uses less digits than its factorization.

20721855 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 277 (or 259 counting only the distinct ones).

The product of its (nonzero) digits is 5600, while the sum is 30.

The square root of 20721855 is about 4552.1264261881. The cubic root of 20721855 is about 274.6689349330.

The spelling of 20721855 in words is "twenty million, seven hundred twenty-one thousand, eight hundred fifty-five".