661743918 has 140 divisors (see below), whose sum is σ = 1689865440. Its totient is φ = 194059800.

The previous prime is 661743911. The next prime is 661743919. The reversal of 661743918 is 819347166.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661743911) by changing a digit.

It is a polite number, since it can be written in 69 ways as a sum of consecutive naturals, for example, 21346563 + ... + 21346593.

Almost surely, 2^661743918 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 661743918, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (844932720).

661743918 is an abundant number, since it is smaller than the sum of its proper divisors (1028121522).

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

661743918 is an frugal number, since it uses more digits than its factorization.

661743918 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 95 (or 47 counting only the distinct ones).

The product of its digits is 217728, while the sum is 45.

The square root of 661743918 is about 25724.3837243966. The cubic root of 661743918 is about 871.4249419155.

The spelling of 661743918 in words is "six hundred sixty-one million, seven hundred forty-three thousand, nine hundred eighteen".