81281818 has 4 divisors (see below), whose sum is σ = 121922730. Its totient is φ = 40640908.

The previous prime is 81281813. The next prime is 81281833. The reversal of 81281818 is 81818218.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 43864129 + 37417689 = 6623^2 + 6117^2 .

It is not an unprimeable number, because it can be changed into a prime (81281813) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20320453 + ... + 20320456.

Almost surely, 2^81281818 is an apocalyptic number.

81281818 is a deficient number, since it is larger than the sum of its proper divisors (40640912).

81281818 is a wasteful number, since it uses less digits than its factorization.

81281818 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40640911.

The product of its digits is 8192, while the sum is 37.

The square root of 81281818 is about 9015.6429609873. The cubic root of 81281818 is about 433.1760827193.

The spelling of 81281818 in words is "eighty-one million, two hundred eighty-one thousand, eight hundred eighteen".