1638385881 has 16 divisors (see below), whose sum is σ = 2383812288. Its totient is φ = 992667200.

The previous prime is 1638385843. The next prime is 1638385883. The reversal of 1638385881 is 1885838361.

It is a cyclic number.

It is not a de Polignac number, because 1638385881 - 2¹⁰ = 1638384857 is a prime.

It is a super-2 number, since 2×1638385881² = 5368616590120292322, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (1638385883) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 168895 + ... + 178331.

It is an arithmetic number, because the mean of its divisors is an integer number (148988268).

Almost surely, 2^1638385881 is an apocalyptic number.

1638385881 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1638385881 is a deficient number, since it is larger than the sum of its proper divisors (745426407).

1638385881 is a wasteful number, since it uses less digits than its factorization.

1638385881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14712.

The product of its digits is 1105920, while the sum is 51.

The square root of 1638385881 is about 40476.9796427550. The cubic root of 1638385881 is about 1178.8866931723.

The spelling of 1638385881 in words is "one billion, six hundred thirty-eight million, three hundred eighty-five thousand, eight hundred eighty-one".