20721977 has 4 divisors (see below), whose sum is σ = 20737536. Its totient is φ = 20706420.

The previous prime is 20721949. The next prime is 20721983. The reversal of 20721977 is 77912702.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 20721977 - 2⁸ = 20721721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20721907) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5573 + ... + 8514.

It is an arithmetic number, because the mean of its divisors is an integer number (5184384).

Almost surely, 2^20721977 is an apocalyptic number.

It is an amenable number.

20721977 is a deficient number, since it is larger than the sum of its proper divisors (15559).

20721977 is a wasteful number, since it uses less digits than its factorization.

20721977 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15558.

The product of its (nonzero) digits is 12348, while the sum is 35.

The square root of 20721977 is about 4552.1398264992. The cubic root of 20721977 is about 274.6694739701.

The spelling of 20721977 in words is "twenty million, seven hundred twenty-one thousand, nine hundred seventy-seven".