661165440 has 128 divisors (see below), whose sum is σ = 2269663200. Its totient is φ = 162742272.

The previous prime is 661165399. The next prime is 661165487. The reversal of 661165440 is 44561166.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (128).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 11716 + ... + 38204.

Almost surely, 2^661165440 is an apocalyptic number.

661165440 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 661165440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1134831600).

661165440 is an abundant number, since it is smaller than the sum of its proper divisors (1608497760).

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

661165440 is a wasteful number, since it uses less digits than its factorization.

661165440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 26524 (or 26512 counting only the distinct ones).

The product of its (nonzero) digits is 17280, while the sum is 33.

The square root of 661165440 is about 25713.1374981740. The cubic root of 661165440 is about 871.1709427952.

The spelling of 661165440 in words is "six hundred sixty-one million, one hundred sixty-five thousand, four hundred forty".