647666221 has 4 divisors (see below), whose sum is σ = 685764252. Its totient is φ = 609568192.

The previous prime is 647666209. The next prime is 647666233. The reversal of 647666221 is 122666746.

647666221 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 122666746 = 2 ⋅61333373.

It is an interprime number because it is at equal distance from previous prime (647666209) and next prime (647666233).

It can be written as a sum of positive squares in 2 ways, for example, as 434097225 + 213568996 = 20835^2 + 14614^2 .

It is a cyclic number.

It is not a de Polignac number, because 647666221 - 2¹⁵ = 647633453 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (647666021) 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, 19048990 + ... + 19049023.

It is an arithmetic number, because the mean of its divisors is an integer number (171441063).

Almost surely, 2^647666221 is an apocalyptic number.

It is an amenable number.

647666221 is a deficient number, since it is larger than the sum of its proper divisors (38098031).

647666221 is a wasteful number, since it uses less digits than its factorization.

647666221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 38098030.

The product of its digits is 145152, while the sum is 40.

The square root of 647666221 is about 25449.2872395279. The cubic root of 647666221 is about 865.2011386978.

The spelling of 647666221 in words is "six hundred forty-seven million, six hundred sixty-six thousand, two hundred twenty-one".