81998731 has 4 divisors (see below), whose sum is σ = 83388600. Its totient is φ = 80608864.

The previous prime is 81998671. The next prime is 81998743. The reversal of 81998731 is 13789918.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 13789918 = 2 ⋅6894959.

It is a cyclic number.

It is not a de Polignac number, because 81998731 - 2⁹ = 81998219 is a prime.

It is a super-2 number, since 2×81998731² = 13447583771220722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81990731) 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, 694846 + ... + 694963.

It is an arithmetic number, because the mean of its divisors is an integer number (20847150).

Almost surely, 2^81998731 is an apocalyptic number.

81998731 is a deficient number, since it is larger than the sum of its proper divisors (1389869).

81998731 is a wasteful number, since it uses less digits than its factorization.

81998731 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1389868.

The product of its digits is 108864, while the sum is 46.

The square root of 81998731 is about 9055.3150690630. The cubic root of 81998731 is about 434.4459074486.

The spelling of 81998731 in words is "eighty-one million, nine hundred ninety-eight thousand, seven hundred thirty-one".