661623666 has 16 divisors (see below), whose sum is σ = 1443542688. Its totient is φ = 200492000.

The previous prime is 661623659. The next prime is 661623667. The reversal of 661623666 is 666326166.

It is a happy number.

It is a super-2 number, since 2×661623666² = 875491750822559112, which contains 22 as substring.

It is a nude number because it is divisible by every one of its digits.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (661623667) 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, 5012235 + ... + 5012366.

It is an arithmetic number, because the mean of its divisors is an integer number (90221418).

Almost surely, 2^661623666 is an apocalyptic number.

661623666 is a gapful number since it is divisible by the number (66) formed by its first and last digit.

661623666 is an abundant number, since it is smaller than the sum of its proper divisors (781919022).

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

661623666 is a wasteful number, since it uses less digits than its factorization.

661623666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10024617.

The product of its digits is 279936, while the sum is 42.

The square root of 661623666 is about 25722.0463027342. The cubic root of 661623666 is about 871.3721536503.

The spelling of 661623666 in words is "six hundred sixty-one million, six hundred twenty-three thousand, six hundred sixty-six".