81491813 has 4 divisors (see below), whose sum is σ = 87760428. Its totient is φ = 75223200.

The previous prime is 81491801. The next prime is 81491833. The reversal of 81491813 is 31819418.

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 13890529 + 67601284 = 3727^2 + 8222^2 .

It is not a de Polignac number, because 81491813 - 2¹⁰ = 81490789 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81491833) 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 3 ways as a sum of consecutive naturals, for example, 3134288 + ... + 3134313.

It is an arithmetic number, because the mean of its divisors is an integer number (21940107).

Almost surely, 2^81491813 is an apocalyptic number.

It is an amenable number.

81491813 is a deficient number, since it is larger than the sum of its proper divisors (6268615).

81491813 is a wasteful number, since it uses less digits than its factorization.

81491813 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6268614.

The product of its digits is 6912, while the sum is 35.

The square root of 81491813 is about 9027.2815952534. The cubic root of 81491813 is about 433.5488048066.

The spelling of 81491813 in words is "eighty-one million, four hundred ninety-one thousand, eight hundred thirteen".