997721 has 4 divisors (see below), whose sum is σ = 1001700. Its totient is φ = 993744.

The previous prime is 997699. The next prime is 997727. The reversal of 997721 is 127799.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 127799 = 7 ⋅18257.

It can be written as a sum of positive squares in 2 ways, for example, as 151321 + 846400 = 389^2 + 920^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-997721 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 10.

It is not an unprimeable number, because it can be changed into a prime (997727) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1586 + ... + 2123.

It is an arithmetic number, because the mean of its divisors is an integer number (250425).

2⁹⁹⁷⁷²¹ is an apocalyptic number.

It is an amenable number.

997721 is a deficient number, since it is larger than the sum of its proper divisors (3979).

997721 is a wasteful number, since it uses less digits than its factorization.

997721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3978.

The product of its digits is 7938, while the sum is 35.

The square root of 997721 is about 998.8598500290. The cubic root of 997721 is about 99.9239755508.

The spelling of 997721 in words is "nine hundred ninety-seven thousand, seven hundred twenty-one".