6666221 has 4 divisors (see below), whose sum is σ = 6672192. Its totient is φ = 6660252.

The previous prime is 6666203. The next prime is 6666223. The reversal of 6666221 is 1226666.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 6666221 - 2⁶ = 6666157 is a prime.

It is a super-3 number, since 3×6666221³ (a number of 21 digits) contains 333 as substring.

It is a Duffinian number.

It is a nialpdrome in base 10.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6666223) 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, 755 + ... + 3728.

It is an arithmetic number, because the mean of its divisors is an integer number (1668048).

Almost surely, 2^6666221 is an apocalyptic number.

It is an amenable number.

6666221 is a deficient number, since it is larger than the sum of its proper divisors (5971).

6666221 is a wasteful number, since it uses less digits than its factorization.

6666221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5970.

The product of its digits is 5184, while the sum is 29.

The square root of 6666221 is about 2581.9025930503. The cubic root of 6666221 is about 188.2030117988.

It can be divided in two parts, 6666 and 221, that multiplied together give a triangular number (1473186 = T₁₇₁₆).

The spelling of 6666221 in words is "six million, six hundred sixty-six thousand, two hundred twenty-one".