666561871 has 4 divisors (see below), whose sum is σ = 669721144. Its totient is φ = 663402600.

The previous prime is 666561859. The next prime is 666561901. The reversal of 666561871 is 178165666.

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

It is a cyclic number.

It is not a de Polignac number, because 666561871 - 2¹⁵ = 666529103 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (666561821) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1579320 + ... + 1579741.

It is an arithmetic number, because the mean of its divisors is an integer number (167430286).

Almost surely, 2^666561871 is an apocalyptic number.

666561871 is a deficient number, since it is larger than the sum of its proper divisors (3159273).

666561871 is a wasteful number, since it uses less digits than its factorization.

666561871 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3159272.

The product of its digits is 362880, while the sum is 46.

The square root of 666561871 is about 25817.8595356005. The cubic root of 666561871 is about 873.5346886141.

The spelling of 666561871 in words is "six hundred sixty-six million, five hundred sixty-one thousand, eight hundred seventy-one".