661166438400 has 1728 divisors, whose sum is σ = 2774327119200. Its totient is φ = 149060321280.

The previous prime is 661166438377. The next prime is 661166438423. The reversal of 661166438400 is 4834661166.

661166438400 is a `hidden beast` number, since 66 + 116 + 6 + 438 + 40 + 0 = 666.

It is an interprime number because it is at equal distance from previous prime (661166438377) and next prime (661166438423).

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 143 ways as a sum of consecutive naturals, for example, 4211251122 + ... + 4211251278.

Almost surely, 2^661166438400 is an apocalyptic number.

661166438400 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 661166438400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1387163559600).

661166438400 is an abundant number, since it is smaller than the sum of its proper divisors (2113160680800).

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

661166438400 is a wasteful number, since it uses less digits than its factorization.

661166438400 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 264 (or 236 counting only the distinct ones).

The product of its (nonzero) digits is 497664, while the sum is 45.

The spelling of 661166438400 in words is "six hundred sixty-one billion, one hundred sixty-six million, four hundred thirty-eight thousand, four hundred".