1638381866 has 12 divisors (see below), whose sum is σ = 2701299426. Its totient is φ = 744718920.

The previous prime is 1638381863. The next prime is 1638381881. The reversal of 1638381866 is 6681838361.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 1370110225 + 268271641 = 37015^2 + 16379^2 .

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (1638381863) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 3384845 + ... + 3385328.

Almost surely, 2^1638381866 is an apocalyptic number.

1638381866 is a deficient number, since it is larger than the sum of its proper divisors (1062917560).

1638381866 is a wasteful number, since it uses less digits than its factorization.

1638381866 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6770197 (or 6770186 counting only the distinct ones).

The product of its digits is 995328, while the sum is 50.

The square root of 1638381866 is about 40476.9300466327. The cubic root of 1638381866 is about 1178.8857301851.

The spelling of 1638381866 in words is "one billion, six hundred thirty-eight million, three hundred eighty-one thousand, eight hundred sixty-six".