81231812 has 6 divisors (see below), whose sum is σ = 142155678. Its totient is φ = 40615904.

The previous prime is 81231767. The next prime is 81231817. The reversal of 81231812 is 21813218.

It can be written as a sum of positive squares in only one way, i.e., 63457156 + 17774656 = 7966^2 + 4216^2 .

It is not an unprimeable number, because it can be changed into a prime (81231817) 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 as a sum of consecutive naturals, namely, 10153973 + ... + 10153980.

It is an arithmetic number, because the mean of its divisors is an integer number (23692613).

Almost surely, 2^81231812 is an apocalyptic number.

It is an amenable number.

81231812 is a deficient number, since it is larger than the sum of its proper divisors (60923866).

81231812 is a wasteful number, since it uses less digits than its factorization.

81231812 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20307957 (or 20307955 counting only the distinct ones).

The product of its digits is 768, while the sum is 26.

The square root of 81231812 is about 9012.8692434762. The cubic root of 81231812 is about 433.0872319882.

The spelling of 81231812 in words is "eighty-one million, two hundred thirty-one thousand, eight hundred twelve".