7920821 has 2 divisors, whose sum is σ = 7920822. Its totient is φ = 7920820.

The previous prime is 7920817. The next prime is 7920833. The reversal of 7920821 is 1280297.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 7365796 + 555025 = 2714^2 + 745^2 .

It is an emirp because it is prime and its reverse (1280297) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 7920821 - 2² = 7920817 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (7920811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3960410 + 3960411.

It is an arithmetic number, because the mean of its divisors is an integer number (3960411).

Almost surely, 2^7920821 is an apocalyptic number.

It is an amenable number.

7920821 is a deficient number, since it is larger than the sum of its proper divisors (1).

7920821 is an equidigital number, since it uses as much as digits as its factorization.

7920821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2016, while the sum is 29.

The square root of 7920821 is about 2814.3953169375. The cubic root of 7920821 is about 199.3379861058.

The spelling of 7920821 in words is "seven million, nine hundred twenty thousand, eight hundred twenty-one".