1666651565666 has 4 divisors (see below), whose sum is σ = 2499977348502. Its totient is φ = 833325782832.

The previous prime is 1666651565617. The next prime is 1666651565669. The reversal of 1666651565666 is 6665651566661.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 1497512665441 + 169138900225 = 1223729^2 + 411265^2 .

It is a super-2 number, since 2×1666651565666² (a number of 25 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (1666651565669) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 416662891415 + ... + 416662891418.

Almost surely, 2^{1666651565666} is an apocalyptic number.

1666651565666 is a deficient number, since it is larger than the sum of its proper divisors (833325782836).

1666651565666 is an equidigital number, since it uses as much as digits as its factorization.

1666651565666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 833325782835.

The product of its digits is 209952000, while the sum is 65.

The spelling of 1666651565666 in words is "one trillion, six hundred sixty-six billion, six hundred fifty-one million, five hundred sixty-five thousand, six hundred sixty-six".