221836721 has 4 divisors (see below), whose sum is σ = 221886192. Its totient is φ = 221787252.

The previous prime is 221836717. The next prime is 221836729. The reversal of 221836721 is 127638122.

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 221836721 - 2² = 221836717 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (221836729) 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, 17255 + ... + 27228.

It is an arithmetic number, because the mean of its divisors is an integer number (55471548).

Almost surely, 2^221836721 is an apocalyptic number.

It is an amenable number.

221836721 is a deficient number, since it is larger than the sum of its proper divisors (49471).

221836721 is an equidigital number, since it uses as much as digits as its factorization.

221836721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 49470.

The product of its digits is 8064, while the sum is 32.

The square root of 221836721 is about 14894.1841334126. The cubic root of 221836721 is about 605.3564104439.

The spelling of 221836721 in words is "two hundred twenty-one million, eight hundred thirty-six thousand, seven hundred twenty-one".