221661021 has 4 divisors (see below), whose sum is σ = 295548032. Its totient is φ = 147774012.

The previous prime is 221661017. The next prime is 221661023. The reversal of 221661021 is 120166122.

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 not a de Polignac number, because 221661021 - 2² = 221661017 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 (221661023) 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, 36943501 + ... + 36943506.

It is an arithmetic number, because the mean of its divisors is an integer number (73887008).

Almost surely, 2^221661021 is an apocalyptic number.

It is an amenable number.

221661021 is a deficient number, since it is larger than the sum of its proper divisors (73887011).

221661021 is an equidigital number, since it uses as much as digits as its factorization.

221661021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 73887010.

The product of its (nonzero) digits is 288, while the sum is 21.

The square root of 221661021 is about 14888.2846896478. The cubic root of 221661021 is about 605.1965493031.

The spelling of 221661021 in words is "two hundred twenty-one million, six hundred sixty-one thousand, twenty-one".