6991021 has 4 divisors (see below), whose sum is σ = 6998044. Its totient is φ = 6984000.

The previous prime is 6991013. The next prime is 6991043. The reversal of 6991021 is 1201996.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 2368521 + 4622500 = 1539^2 + 2150^2 .

It is a cyclic number.

It is not a de Polignac number, because 6991021 - 2³ = 6991013 is a prime.

It is a Duffinian number.

6991021 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6991091) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1710 + ... + 4111.

It is an arithmetic number, because the mean of its divisors is an integer number (1749511).

Almost surely, 2^6991021 is an apocalyptic number.

It is an amenable number.

6991021 is a deficient number, since it is larger than the sum of its proper divisors (7023).

6991021 is a wasteful number, since it uses less digits than its factorization.

6991021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7022.

The product of its (nonzero) digits is 972, while the sum is 28.

The square root of 6991021 is about 2644.0538950634. The cubic root of 6991021 is about 191.2112918087.

The spelling of 6991021 in words is "six million, nine hundred ninety-one thousand, twenty-one".