81491773 has 4 divisors (see below), whose sum is σ = 88900128. Its totient is φ = 74083420.

The previous prime is 81491771. The next prime is 81491801. The reversal of 81491773 is 37719418.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 81491773 - 2¹ = 81491771 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81491771) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3704161 + ... + 3704182.

It is an arithmetic number, because the mean of its divisors is an integer number (22225032).

Almost surely, 2^81491773 is an apocalyptic number.

It is an amenable number.

81491773 is a deficient number, since it is larger than the sum of its proper divisors (7408355).

81491773 is a wasteful number, since it uses less digits than its factorization.

81491773 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7408354.

The product of its digits is 42336, while the sum is 40.

The square root of 81491773 is about 9027.2793797467. The cubic root of 81491773 is about 433.5487338712.

The spelling of 81491773 in words is "eighty-one million, four hundred ninety-one thousand, seven hundred seventy-three".