221998661 has 4 divisors (see below), whose sum is σ = 222074112. Its totient is φ = 221923212.

The previous prime is 221998639. The next prime is 221998787. The reversal of 221998661 is 166899122.

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 221998661 - 2¹⁰ = 221997637 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 (221997661) 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, 33125 + ... + 39258.

It is an arithmetic number, because the mean of its divisors is an integer number (55518528).

Almost surely, 2^221998661 is an apocalyptic number.

It is an amenable number.

221998661 is a deficient number, since it is larger than the sum of its proper divisors (75451).

221998661 is an equidigital number, since it uses as much as digits as its factorization.

221998661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 75450.

The product of its digits is 93312, while the sum is 44.

The square root of 221998661 is about 14899.6194917857. The cubic root of 221998661 is about 605.5036772747.

The spelling of 221998661 in words is "two hundred twenty-one million, nine hundred ninety-eight thousand, six hundred sixty-one".