6720021 has 24 divisors (see below), whose sum is σ = 12103104. Its totient is φ = 3490560.

The previous prime is 6720011. The next prime is 6720047. The reversal of 6720021 is 1200276.

It is a happy number.

It is not a de Polignac number, because 6720021 - 2⁵ = 6719989 is a prime.

It is a Curzon number.

6720021 is a lucky number.

It is a junction number, because it is equal to n+sod(n) for n = 6719976 and 6720003.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6720011) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 4156 + ... + 5541.

It is an arithmetic number, because the mean of its divisors is an integer number (504296).

Almost surely, 2^6720021 is an apocalyptic number.

6720021 is the 1386-th nonagonal number.

It is an amenable number.

6720021 is a deficient number, since it is larger than the sum of its proper divisors (5383083).

6720021 is a wasteful number, since it uses less digits than its factorization.

6720021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9721 (or 9718 counting only the distinct ones).

The product of its (nonzero) digits is 168, while the sum is 18.

The square root of 6720021 is about 2592.3003298229. The cubic root of 6720021 is about 188.7079557830.

Adding to 6720021 its reverse (1200276), we get a palindrome (7920297).

It can be divided in two parts, 6 and 720021, that added together give a palindrome (720027).

The spelling of 6720021 in words is "six million, seven hundred twenty thousand, twenty-one".