81451813 has 4 divisors (see below), whose sum is σ = 81470988. Its totient is φ = 81432640.

The previous prime is 81451793. The next prime is 81451819. The reversal of 81451813 is 31815418.

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 18122049 + 63329764 = 4257^2 + 7958^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81451813 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81451819) 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, 58 + ... + 12763.

It is an arithmetic number, because the mean of its divisors is an integer number (20367747).

Almost surely, 2^81451813 is an apocalyptic number.

It is an amenable number.

81451813 is a deficient number, since it is larger than the sum of its proper divisors (19175).

81451813 is a wasteful number, since it uses less digits than its factorization.

81451813 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19174.

The product of its digits is 3840, while the sum is 31.

The square root of 81451813 is about 9025.0658169345. The cubic root of 81451813 is about 433.4778578418.

The spelling of 81451813 in words is "eighty-one million, four hundred fifty-one thousand, eight hundred thirteen".