81878391 has 48 divisors (see below), whose sum is σ = 146899200. Its totient is φ = 44031600.

The previous prime is 81878389. The next prime is 81878393. The reversal of 81878391 is 19387818.

It is an interprime number because it is at equal distance from previous prime (81878389) and next prime (81878393).

It is not a de Polignac number, because 81878391 - 2¹ = 81878389 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81878393) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 542166 + ... + 542316.

It is an arithmetic number, because the mean of its divisors is an integer number (3060400).

Almost surely, 2^81878391 is an apocalyptic number.

81878391 is a deficient number, since it is larger than the sum of its proper divisors (65020809).

81878391 is a wasteful number, since it uses less digits than its factorization.

81878391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 337 (or 180 counting only the distinct ones).

The product of its digits is 96768, while the sum is 45.

The square root of 81878391 is about 9048.6679130135. The cubic root of 81878391 is about 434.2332748204.

The spelling of 81878391 in words is "eighty-one million, eight hundred seventy-eight thousand, three hundred ninety-one".