81813881 has 2 divisors, whose sum is σ = 81813882. Its totient is φ = 81813880.

The previous prime is 81813869. The next prime is 81813883. The reversal of 81813881 is 18831818.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 81288256 + 525625 = 9016^2 + 725^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81813881 is a prime.

It is a super-2 number, since 2×81813881² = 13387022248564322, which contains 22 as substring.

Together with 81813883, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (81813883) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40906940 + 40906941.

It is an arithmetic number, because the mean of its divisors is an integer number (40906941).

Almost surely, 2^81813881 is an apocalyptic number.

It is an amenable number.

81813881 is a deficient number, since it is larger than the sum of its proper divisors (1).

81813881 is an equidigital number, since it uses as much as digits as its factorization.

81813881 is an evil number, because the sum of its binary digits is even.

The product of its digits is 12288, while the sum is 38.

The square root of 81813881 is about 9045.1025975386. The cubic root of 81813881 is about 434.1192042327.

The spelling of 81813881 in words is "eighty-one million, eight hundred thirteen thousand, eight hundred eighty-one".