81911765 has 48 divisors (see below), whose sum is σ = 113840640. Its totient is φ = 56459520.

The previous prime is 81911761. The next prime is 81911771. The reversal of 81911765 is 56711918.

It is not a de Polignac number, because 81911765 - 2² = 81911761 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81911761) 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 47 ways as a sum of consecutive naturals, for example, 1388306 + ... + 1388364.

It is an arithmetic number, because the mean of its divisors is an integer number (2371680).

Almost surely, 2^81911765 is an apocalyptic number.

It is an amenable number.

81911765 is a deficient number, since it is larger than the sum of its proper divisors (31928875).

81911765 is a wasteful number, since it uses less digits than its factorization.

81911765 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 174 (or 161 counting only the distinct ones).

The product of its digits is 15120, while the sum is 38.

The square root of 81911765 is about 9050.5118639776. The cubic root of 81911765 is about 434.2922652840.

The spelling of 81911765 in words is "eighty-one million, nine hundred eleven thousand, seven hundred sixty-five".