997661981 has 8 divisors (see below), whose sum is σ = 1001824824. Its totient is φ = 993507840.

The previous prime is 997661957. The next prime is 997661989. The reversal of 997661981 is 189166799.

It can be written as a sum of positive squares in 4 ways, for example, as 81631225 + 916030756 = 9035^2 + 30266^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-997661981 is a prime.

It is a super-2 number, since 2×997661981² = 1990658856665688722, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (997661989) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 318101 + ... + 321221.

It is an arithmetic number, because the mean of its divisors is an integer number (125228103).

Almost surely, 2^997661981 is an apocalyptic number.

It is an amenable number.

997661981 is a deficient number, since it is larger than the sum of its proper divisors (4162843).

997661981 is a wasteful number, since it uses less digits than its factorization.

997661981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4351.

The product of its digits is 1469664, while the sum is 56.

The square root of 997661981 is about 31585.7876425458. The cubic root of 997661981 is about 999.2200521729.

The spelling of 997661981 in words is "nine hundred ninety-seven million, six hundred sixty-one thousand, nine hundred eighty-one".