661916640 has 192 divisors, whose sum is σ = 2599672320. Its totient is φ = 137533440.

The previous prime is 661916621. The next prime is 661916653. The reversal of 661916640 is 46619166.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 28006 + ... + 45914.

It is an arithmetic number, because the mean of its divisors is an integer number (13539960).

Almost surely, 2^661916640 is an apocalyptic number.

661916640 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 661916640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1299836160).

661916640 is an abundant number, since it is smaller than the sum of its proper divisors (1937755680).

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

661916640 is a wasteful number, since it uses less digits than its factorization.

661916640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17945 (or 17937 counting only the distinct ones).

The product of its (nonzero) digits is 46656, while the sum is 39.

The square root of 661916640 is about 25727.7406703348. The cubic root of 661916640 is about 871.5007522914.

The spelling of 661916640 in words is "six hundred sixty-one million, nine hundred sixteen thousand, six hundred forty".