81773991 has 12 divisors (see below), whose sum is σ = 127204168. Its totient is φ = 50322384.

The previous prime is 81773987. The next prime is 81774013. The reversal of 81773991 is 19937718.

It is not a de Polignac number, because 81773991 - 2² = 81773987 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81773911) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 349345 + ... + 349578.

Almost surely, 2^81773991 is an apocalyptic number.

81773991 is a deficient number, since it is larger than the sum of its proper divisors (45430177).

81773991 is a wasteful number, since it uses less digits than its factorization.

81773991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 698942 (or 698939 counting only the distinct ones).

The product of its digits is 95256, while the sum is 45.

The square root of 81773991 is about 9042.8972680220. The cubic root of 81773991 is about 434.0486382520.

The spelling of 81773991 in words is "eighty-one million, seven hundred seventy-three thousand, nine hundred ninety-one".