661728666 has 16 divisors (see below), whose sum is σ = 1366149888. Its totient is φ = 213460800.

The previous prime is 661728629. The next prime is 661728667. The reversal of 661728666 is 666827166.

It is a super-2 number, since 2×661728666² = 875769654812279112, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (661728667) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1778655 + ... + 1779026.

It is an arithmetic number, because the mean of its divisors is an integer number (85384368).

Almost surely, 2^661728666 is an apocalyptic number.

661728666 is an abundant number, since it is smaller than the sum of its proper divisors (704421222).

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

661728666 is a wasteful number, since it uses less digits than its factorization.

661728666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3557717.

The product of its digits is 870912, while the sum is 48.

The square root of 661728666 is about 25724.0872724379. The cubic root of 661728666 is about 871.4182469413.

The spelling of 661728666 in words is "six hundred sixty-one million, seven hundred twenty-eight thousand, six hundred sixty-six".