81185173 has 4 divisors (see below), whose sum is σ = 82396960. Its totient is φ = 79973388.

The previous prime is 81185129. The next prime is 81185179. The reversal of 81185173 is 37158118.

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, and also an emirpimes, since its reverse is a distinct semiprime: 37158118 = 2 ⋅18579059.

It is a cyclic number.

It is not a de Polignac number, because 81185173 - 2²¹ = 79088021 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 (81185179) 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, 605793 + ... + 605926.

It is an arithmetic number, because the mean of its divisors is an integer number (20599240).

Almost surely, 2^81185173 is an apocalyptic number.

It is an amenable number.

81185173 is a deficient number, since it is larger than the sum of its proper divisors (1211787).

81185173 is a wasteful number, since it uses less digits than its factorization.

81185173 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1211786.

The product of its digits is 6720, while the sum is 34.

The square root of 81185173 is about 9010.2815161348. The cubic root of 81185173 is about 433.0043308774.

The spelling of 81185173 in words is "eighty-one million, one hundred eighty-five thousand, one hundred seventy-three".