81398731 has 4 divisors (see below), whose sum is σ = 82545264. Its totient is φ = 80252200.

The previous prime is 81398729. The next prime is 81398741. The reversal of 81398731 is 13789318.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 81398731 - 2¹ = 81398729 is a prime.

It is a super-2 number, since 2×81398731² = 13251506816820722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81398741) 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, 573160 + ... + 573301.

It is an arithmetic number, because the mean of its divisors is an integer number (20636316).

Almost surely, 2^81398731 is an apocalyptic number.

81398731 is a deficient number, since it is larger than the sum of its proper divisors (1146533).

81398731 is a wasteful number, since it uses less digits than its factorization.

81398731 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1146532.

The product of its digits is 36288, while the sum is 40.

The square root of 81398731 is about 9022.1245280699. The cubic root of 81398731 is about 433.3836717985.

The spelling of 81398731 in words is "eighty-one million, three hundred ninety-eight thousand, seven hundred thirty-one".