1665638400 has 168 divisors, whose sum is σ = 5509406304. Its totient is φ = 444006400.

The previous prime is 1665638399. The next prime is 1665638437. The reversal of 1665638400 is 48365661.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 613045 + ... + 615755.

Almost surely, 2^1665638400 is an apocalyptic number.

1665638400 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 1665638400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2754703152).

1665638400 is an abundant number, since it is smaller than the sum of its proper divisors (3843767904).

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

1665638400 is an equidigital number, since it uses as much as digits as its factorization.

1665638400 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2750 (or 2721 counting only the distinct ones).

The product of its (nonzero) digits is 103680, while the sum is 39.

The square root of 1665638400 is about 40812.2334600791. The cubic root of 1665638400 is about 1185.3872223471.

The spelling of 1665638400 in words is "one billion, six hundred sixty-five million, six hundred thirty-eight thousand, four hundred".