81800066 has 4 divisors (see below), whose sum is σ = 122700102. Its totient is φ = 40900032.

The previous prime is 81800063. The next prime is 81800071. The reversal of 81800066 is 66000818.

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., 43099225 + 38700841 = 6565^2 + 6221^2 .

It is not an unprimeable number, because it can be changed into a prime (81800063) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20450015 + ... + 20450018.

Almost surely, 2^81800066 is an apocalyptic number.

81800066 is a deficient number, since it is larger than the sum of its proper divisors (40900036).

81800066 is a wasteful number, since it uses less digits than its factorization.

81800066 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40900035.

The product of its (nonzero) digits is 2304, while the sum is 29.

The square root of 81800066 is about 9044.3388923680. The cubic root of 81800066 is about 434.0947678969.

The spelling of 81800066 in words is "eighty-one million, eight hundred thousand, sixty-six".