81891375 has 32 divisors (see below), whose sum is σ = 137389824. Its totient is φ = 43316000.

The previous prime is 81891371. The next prime is 81891379. The reversal of 81891375 is 57319818.

It is an interprime number because it is at equal distance from previous prime (81891371) and next prime (81891379).

It is not a de Polignac number, because 81891375 - 2² = 81891371 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81891371) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 48292 + ... + 49958.

It is an arithmetic number, because the mean of its divisors is an integer number (4293432).

Almost surely, 2^81891375 is an apocalyptic number.

81891375 is a deficient number, since it is larger than the sum of its proper divisors (55498449).

81891375 is a wasteful number, since it uses less digits than its factorization.

81891375 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1816 (or 1806 counting only the distinct ones).

The product of its digits is 60480, while the sum is 42.

The square root of 81891375 is about 9049.3853382426. The cubic root of 81891375 is about 434.2562266915.

The spelling of 81891375 in words is "eighty-one million, eight hundred ninety-one thousand, three hundred seventy-five".