6640400 has 60 divisors (see below), whose sum is σ = 17194212. Its totient is φ = 2449920.

The previous prime is 6640397. The next prime is 6640409. The reversal of 6640400 is 40466.

It can be written as a sum of positive squares in 6 ways, for example, as 430336 + 6210064 = 656^2 + 2492^2 .

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a nialpdrome in base 16.

It is not an unprimeable number, because it can be changed into a prime (6640409) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 4562 + ... + 5838.

Almost surely, 2^6640400 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 6640400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (8597106).

6640400 is an abundant number, since it is smaller than the sum of its proper divisors (10553812).

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

6640400 is a wasteful number, since it uses less digits than its factorization.

6640400 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1308 (or 1297 counting only the distinct ones).

The product of its (nonzero) digits is 576, while the sum is 20.

The square root of 6640400 is about 2576.8973592287. The cubic root of 6640400 is about 187.9597016387.

Adding to 6640400 its reverse (40466), we get a palindrome (6680866).

The spelling of 6640400 in words is "six million, six hundred forty thousand, four hundred".