81990113 has 4 divisors (see below), whose sum is σ = 84206100. Its totient is φ = 79774128.

The previous prime is 81990107. The next prime is 81990143. The reversal of 81990113 is 31109918.

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

It can be written as a sum of positive squares in 2 ways, for example, as 51165409 + 30824704 = 7153^2 + 5552^2 .

It is a cyclic number.

It is not a de Polignac number, because 81990113 - 2⁶ = 81990049 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81990113.

It is not an unprimeable number, because it can be changed into a prime (81990143) 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, 1107938 + ... + 1108011.

It is an arithmetic number, because the mean of its divisors is an integer number (21051525).

Almost surely, 2^81990113 is an apocalyptic number.

It is an amenable number.

81990113 is a deficient number, since it is larger than the sum of its proper divisors (2215987).

81990113 is a wasteful number, since it uses less digits than its factorization.

81990113 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2215986.

The product of its (nonzero) digits is 1944, while the sum is 32.

The square root of 81990113 is about 9054.8392034315. The cubic root of 81990113 is about 434.4306869448.

The spelling of 81990113 in words is "eighty-one million, nine hundred ninety thousand, one hundred thirteen".