81181213 has 4 divisors (see below), whose sum is σ = 82712988. Its totient is φ = 79649440.

The previous prime is 81181211. The next prime is 81181223. The reversal of 81181213 is 31218118.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 31218118 = 2 ⋅15609059.

It can be written as a sum of positive squares in 2 ways, for example, as 30173049 + 51008164 = 5493^2 + 7142^2 .

It is a cyclic number.

It is not a de Polignac number, because 81181213 - 2¹ = 81181211 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 (81181211) 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, 765808 + ... + 765913.

It is an arithmetic number, because the mean of its divisors is an integer number (20678247).

Almost surely, 2^81181213 is an apocalyptic number.

It is an amenable number.

81181213 is a deficient number, since it is larger than the sum of its proper divisors (1531775).

81181213 is a wasteful number, since it uses less digits than its factorization.

81181213 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1531774.

The product of its digits is 384, while the sum is 25.

The square root of 81181213 is about 9010.0617644942. The cubic root of 81181213 is about 432.9972904908.

The spelling of 81181213 in words is "eighty-one million, one hundred eighty-one thousand, two hundred thirteen".