81993987 has 12 divisors (see below), whose sum is σ = 124669480. Its totient is φ = 51785568.

The previous prime is 81993983. The next prime is 81994001. The reversal of 81993987 is 78939918.

It is not a de Polignac number, because 81993987 - 2² = 81993983 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81993983) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 239578 + ... + 239919.

Almost surely, 2^81993987 is an apocalyptic number.

81993987 is a deficient number, since it is larger than the sum of its proper divisors (42675493).

81993987 is a wasteful number, since it uses less digits than its factorization.

81993987 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 479522 (or 479519 counting only the distinct ones).

The product of its digits is 979776, while the sum is 54.

The square root of 81993987 is about 9055.0531196675. The cubic root of 81993987 is about 434.4375290623.

The spelling of 81993987 in words is "eighty-one million, nine hundred ninety-three thousand, nine hundred eighty-seven".