6697621921 has 3 divisors (see below), whose sum is σ = 6697703761. Its totient is φ = 6697540082.

The previous prime is 6697621883. The next prime is 6697621927. The reversal of 6697621921 is 1291267966.

It is a happy number.

The square root of 6697621921 is 81839.

It is a perfect power (a square), and thus also a powerful number.

6697621921 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

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, and also an emirpimes, since its reverse is a distinct semiprime: 1291267966 = 2 ⋅645633983.

It is not a de Polignac number, because 6697621921 - 2⁹ = 6697621409 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (6697621927) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 40920 + ... + 122758.

Almost surely, 2^6697621921 is an apocalyptic number.

6697621921 is the 81839-th square number.

6697621921 is the 40920-th centered octagonal number.

It is an amenable number.

6697621921 is a deficient number, since it is larger than the sum of its proper divisors (81840).

6697621921 is an frugal number, since it uses more digits than its factorization.

6697621921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 163678 (or 81839 counting only the distinct ones).

The product of its digits is 489888, while the sum is 49.

The cubic root of 6697621921 is about 1884.9805616835.

Multiplying 6697621921 by its sum of digits (49), we get a square (328183474129 = 572873²).

The spelling of 6697621921 in words is "six billion, six hundred ninety-seven million, six hundred twenty-one thousand, nine hundred twenty-one".