221666 has 8 divisors (see below), whose sum is σ = 335340. Its totient is φ = 109888.

The previous prime is 221659. The next prime is 221671. The reversal of 221666 is 666122.

221666 is digitally balanced in base 2 and base 3, because in such bases it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 2 ways, for example, as 207025 + 14641 = 455^2 + 121^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 131 + ... + 678.

2²²¹⁶⁶⁶ is an apocalyptic number.

221666 is a deficient number, since it is larger than the sum of its proper divisors (113674).

221666 is a wasteful number, since it uses less digits than its factorization.

221666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 948.

The product of its digits is 864, while the sum is 23.

The square root of 221666 is about 470.8141884013. The cubic root of 221666 is about 60.5201080623.

Adding to 221666 its reverse (666122), we get a palindrome (887788).

The spelling of 221666 in words is "two hundred twenty-one thousand, six hundred sixty-six".