997855721 has 4 divisors (see below), whose sum is σ = 1021061712. Its totient is φ = 974649732.

The previous prime is 997855717. The next prime is 997855753. The reversal of 997855721 is 127558799.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 997855721 - 2² = 997855717 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (997855711) 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 3 ways as a sum of consecutive naturals, for example, 11602931 + ... + 11603016.

It is an arithmetic number, because the mean of its divisors is an integer number (255265428).

Almost surely, 2^997855721 is an apocalyptic number.

It is an amenable number.

997855721 is a deficient number, since it is larger than the sum of its proper divisors (23205991).

997855721 is a wasteful number, since it uses less digits than its factorization.

997855721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23205990.

The product of its digits is 1587600, while the sum is 53.

The square root of 997855721 is about 31588.8543793535. The cubic root of 997855721 is about 999.2847288425.

The spelling of 997855721 in words is "nine hundred ninety-seven million, eight hundred fifty-five thousand, seven hundred twenty-one".