81387891 has 72 divisors (see below), whose sum is σ = 140802480. Its totient is φ = 44964864.

The previous prime is 81387881. The next prime is 81387893. The reversal of 81387891 is 19878318.

It is not a de Polignac number, because 81387891 - 2¹³ = 81379699 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81387893) by changing a digit.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 980536 + ... + 980618.

It is an arithmetic number, because the mean of its divisors is an integer number (1955590).

Almost surely, 2^81387891 is an apocalyptic number.

81387891 is a deficient number, since it is larger than the sum of its proper divisors (59414589).

81387891 is a wasteful number, since it uses less digits than its factorization.

81387891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 165 (or 145 counting only the distinct ones).

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

The square root of 81387891 is about 9021.5237626468. The cubic root of 81387891 is about 433.3644328107.

The spelling of 81387891 in words is "eighty-one million, three hundred eighty-seven thousand, eight hundred ninety-one".