661820400 has 180 divisors, whose sum is σ = 2396857008. Its totient is φ = 168791040.

The previous prime is 661820399. The next prime is 661820429. The reversal of 661820400 is 4028166.

661820400 is a `hidden beast` number, since 6 + 618 + 2 + 0 + 40 + 0 = 666.

It is a tau number, because it is divible by the number of its divisors (180).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 78804 + ... + 86796.

Almost surely, 2^661820400 is an apocalyptic number.

661820400 is a gapful number since it is divisible by the number (60) 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 661820400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1198428504).

661820400 is an abundant number, since it is smaller than the sum of its proper divisors (1735036608).

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

661820400 is a wasteful number, since it uses less digits than its factorization.

661820400 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8040 (or 8026 counting only the distinct ones).

The product of its (nonzero) digits is 2304, while the sum is 27.

The square root of 661820400 is about 25725.8702476709. The cubic root of 661820400 is about 871.4585126836.

Adding to 661820400 its reverse (4028166), we get a palindrome (665848566).

The spelling of 661820400 in words is "six hundred sixty-one million, eight hundred twenty thousand, four hundred".