399781818 has 40 divisors (see below), whose sum is σ = 920032212. Its totient is φ = 129657024.

The previous prime is 399781813. The next prime is 399781819. The reversal of 399781818 is 818187993.

399781818 is a `hidden beast` number, since 399 + 78 + 181 + 8 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 393109929 + 6671889 = 19827^2 + 2583^2 .

It is a Harshad number since it is a multiple of its sum of digits (54).

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (399781813) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 27355 + ... + 39342.

Almost surely, 2^399781818 is an apocalyptic number.

399781818 is an abundant number, since it is smaller than the sum of its proper divisors (520250394).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

399781818 is a wasteful number, since it uses less digits than its factorization.

399781818 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 66748 (or 66739 counting only the distinct ones).

The product of its digits is 870912, while the sum is 54.

The square root of 399781818 is about 19994.5447059942. The cubic root of 399781818 is about 736.6723104700.

The spelling of 399781818 in words is "three hundred ninety-nine million, seven hundred eighty-one thousand, eight hundred eighteen".