81911807 has 4 divisors (see below), whose sum is σ = 81972840. Its totient is φ = 81850776.

The previous prime is 81911771. The next prime is 81911813. The reversal of 81911807 is 70811918.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 81911807 - 2⁶ = 81911743 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 (81911887) 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, 28457 + ... + 31202.

It is an arithmetic number, because the mean of its divisors is an integer number (20493210).

Almost surely, 2^81911807 is an apocalyptic number.

81911807 is a deficient number, since it is larger than the sum of its proper divisors (61033).

81911807 is a wasteful number, since it uses less digits than its factorization.

81911807 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 61032.

The product of its (nonzero) digits is 4032, while the sum is 35.

The square root of 81911807 is about 9050.5141842881. The cubic root of 81911807 is about 434.2923395113.

The spelling of 81911807 in words is "eighty-one million, nine hundred eleven thousand, eight hundred seven".