998637781 has 4 divisors (see below), whose sum is σ = 998707564. Its totient is φ = 998568000.

The previous prime is 998637769. The next prime is 998637797. The reversal of 998637781 is 187736899.

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.

It can be written as a sum of positive squares in 2 ways, for example, as 558896881 + 439740900 = 23641^2 + 20970^2 .

It is a cyclic number.

It is not a de Polignac number, because 998637781 - 2¹⁷ = 998506709 is a prime.

It is a super-2 number, since 2×998637781² = 1994554835281207922, 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 (998637721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4740 + ... + 44941.

It is an arithmetic number, because the mean of its divisors is an integer number (249676891).

Almost surely, 2^998637781 is an apocalyptic number.

998637781 is the 14133-rd centered decagonal number.

It is an amenable number.

998637781 is a deficient number, since it is larger than the sum of its proper divisors (69783).

998637781 is a wasteful number, since it uses less digits than its factorization.

998637781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 69782.

The product of its digits is 4572288, while the sum is 58.

The square root of 998637781 is about 31601.2306880602. The cubic root of 998637781 is about 999.5457206615.

The spelling of 998637781 in words is "nine hundred ninety-eight million, six hundred thirty-seven thousand, seven hundred eighty-one".