997659781 has 4 divisors (see below), whose sum is σ = 999824364. Its totient is φ = 995495200.

The previous prime is 997659731. The next prime is 997659787. The reversal of 997659781 is 187956799.

997659781 = 22334² + 22335².

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 187956799 = 61 ⋅3081259.

It can be written as a sum of positive squares in 2 ways, for example, as 498852225 + 498807556 = 22335^2 + 22334^2 .

It is a cyclic number.

It is not a de Polignac number, because 997659781 - 2²⁵ = 964105349 is a prime.

It is a super-2 number, since 2×997659781² = 1990650077249935922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (997659787) 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, 1081600 + ... + 1082521.

It is an arithmetic number, because the mean of its divisors is an integer number (249956091).

Almost surely, 2^997659781 is an apocalyptic number.

997659781 is the 22335-th centered square number.

It is an amenable number.

997659781 is a deficient number, since it is larger than the sum of its proper divisors (2164583).

997659781 is a wasteful number, since it uses less digits than its factorization.

997659781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2164582.

The product of its digits is 8573040, while the sum is 61.

The square root of 997659781 is about 31585.7528167369. The cubic root of 997659781 is about 999.2193176937.

The spelling of 997659781 in words is "nine hundred ninety-seven million, six hundred fifty-nine thousand, seven hundred eighty-one".