666551566 has 4 divisors (see below), whose sum is σ = 999827352. Its totient is φ = 333275782.

The previous prime is 666551551. The next prime is 666551591. The reversal of 666551566 is 665155666.

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

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 166637890 + ... + 166637893.

It is an arithmetic number, because the mean of its divisors is an integer number (249956838).

Almost surely, 2^666551566 is an apocalyptic number.

666551566 is a deficient number, since it is larger than the sum of its proper divisors (333275786).

666551566 is a wasteful number, since it uses less digits than its factorization.

666551566 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 333275785.

The product of its digits is 972000, while the sum is 46.

The square root of 666551566 is about 25817.6599636760. The cubic root of 666551566 is about 873.5301869957.

The spelling of 666551566 in words is "six hundred sixty-six million, five hundred fifty-one thousand, five hundred sixty-six".