210666661 has 4 divisors (see below), whose sum is σ = 221754400. Its totient is φ = 199578924.

The previous prime is 210666619. The next prime is 210666667. The reversal of 210666661 is 166666012.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 210666661 - 2²¹ = 208569509 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 (210666667) 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, 5543841 + ... + 5543878.

It is an arithmetic number, because the mean of its divisors is an integer number (55438600).

Almost surely, 2^210666661 is an apocalyptic number.

It is an amenable number.

210666661 is a deficient number, since it is larger than the sum of its proper divisors (11087739).

210666661 is a wasteful number, since it uses less digits than its factorization.

210666661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11087738.

The product of its (nonzero) digits is 15552, while the sum is 34.

The square root of 210666661 is about 14514.3605095092. The cubic root of 210666661 is about 595.0205119685.

The spelling of 210666661 in words is "two hundred ten million, six hundred sixty-six thousand, six hundred sixty-one".