20721955 has 8 divisors (see below), whose sum is σ = 25062912. Its totient is φ = 16446528.

The previous prime is 20721949. The next prime is 20721983. The reversal of 20721955 is 55912702.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 20721955 - 2³ = 20721947 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 15682 + ... + 16951.

It is an arithmetic number, because the mean of its divisors is an integer number (3132864).

Almost surely, 2^20721955 is an apocalyptic number.

20721955 is a deficient number, since it is larger than the sum of its proper divisors (4340957).

20721955 is a wasteful number, since it uses less digits than its factorization.

20721955 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32765.

The product of its (nonzero) digits is 6300, while the sum is 31.

The square root of 20721955 is about 4552.1374100526. The cubic root of 20721955 is about 274.6693767668.

The spelling of 20721955 in words is "twenty million, seven hundred twenty-one thousand, nine hundred fifty-five".