221978921 has 2 divisors, whose sum is σ = 221978922. Its totient is φ = 221978920.

The previous prime is 221978917. The next prime is 221978923. The reversal of 221978921 is 129879122.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 162919696 + 59059225 = 12764^2 + 7685^2 .

It is a cyclic number.

It is not a de Polignac number, because 221978921 - 2² = 221978917 is a prime.

Together with 221978923, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (221978923) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 110989460 + 110989461.

It is an arithmetic number, because the mean of its divisors is an integer number (110989461).

Almost surely, 2^221978921 is an apocalyptic number.

It is an amenable number.

221978921 is a deficient number, since it is larger than the sum of its proper divisors (1).

221978921 is an equidigital number, since it uses as much as digits as its factorization.

221978921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 36288, while the sum is 41.

The square root of 221978921 is about 14898.9570440350. The cubic root of 221978921 is about 605.4857297237.

The spelling of 221978921 in words is "two hundred twenty-one million, nine hundred seventy-eight thousand, nine hundred twenty-one".