7999921 has 2 divisors, whose sum is σ = 7999922. Its totient is φ = 7999920.

The previous prime is 7999919. The next prime is 7999963. The reversal of 7999921 is 1299997.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 5640625 + 2359296 = 2375^2 + 1536^2 .

It is a cyclic number.

It is not a de Polignac number, because 7999921 - 2¹ = 7999919 is a prime.

Together with 7999919, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (7909921) by changing a digit.

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 as a sum of consecutive naturals, namely, 3999960 + 3999961.

It is an arithmetic number, because the mean of its divisors is an integer number (3999961).

Almost surely, 2^7999921 is an apocalyptic number.

It is an amenable number.

7999921 is a deficient number, since it is larger than the sum of its proper divisors (1).

7999921 is an equidigital number, since it uses as much as digits as its factorization.

7999921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 91854, while the sum is 46.

The square root of 7999921 is about 2828.4131593528. The cubic root of 7999921 is about 199.9993416645. Note that the first 3 decimals are identical.

It can be divided in two parts, 79 and 99921, that added together give a 5-th power (100000 = 10⁵).

The spelling of 7999921 in words is "seven million, nine hundred ninety-nine thousand, nine hundred twenty-one".