81308218 has 4 divisors (see below), whose sum is σ = 121962330. Its totient is φ = 40654108.

The previous prime is 81308191. The next prime is 81308221. The reversal of 81308218 is 81280318.

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., 77035729 + 4272489 = 8777^2 + 2067^2 .

It is a super-2 number, since 2×81308218² = 13222052628671048, which contains 22 as substring.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a self number, because there is not a number n which added to its sum of digits gives 81308218.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20327053 + ... + 20327056.

Almost surely, 2^81308218 is an apocalyptic number.

81308218 is a deficient number, since it is larger than the sum of its proper divisors (40654112).

81308218 is a wasteful number, since it uses less digits than its factorization.

81308218 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40654111.

The product of its (nonzero) digits is 3072, while the sum is 31.

The square root of 81308218 is about 9017.1069639880. The cubic root of 81308218 is about 433.2229755792. Note that the first 3 decimals are identical.

The spelling of 81308218 in words is "eighty-one million, three hundred eight thousand, two hundred eighteen".