661537800 has 768 divisors, whose sum is σ = 2985523200. Its totient is φ = 130636800.

The previous prime is 661537781. The next prime is 661537819. The reversal of 661537800 is 8735166.

661537800 is a `hidden beast` number, since 6 + 615 + 37 + 8 + 0 + 0 = 666.

It is an interprime number because it is at equal distance from previous prime (661537781) and next prime (661537819).

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 191 ways as a sum of consecutive naturals, for example, 15384579 + ... + 15384621.

It is an arithmetic number, because the mean of its divisors is an integer number (3887400).

Almost surely, 2^661537800 is an apocalyptic number.

661537800 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

661537800 is the 14850-th octagonal number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 661537800, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1492761600).

661537800 is an abundant number, since it is smaller than the sum of its proper divisors (2323985400).

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

661537800 is a wasteful number, since it uses less digits than its factorization.

661537800 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 123 (or 108 counting only the distinct ones).

The product of its (nonzero) digits is 30240, while the sum is 36.

The square root of 661537800 is about 25720.3771356487. The cubic root of 661537800 is about 871.3344562491.

It can be divided in two parts, 6615 and 37800, that multiplied together give a cube (250047000 = 630³).

The spelling of 661537800 in words is "six hundred sixty-one million, five hundred thirty-seven thousand, eight hundred".