221100021 has 6 divisors (see below), whose sum is σ = 319366710. Its totient is φ = 147400008.

The previous prime is 221099999. The next prime is 221100037. The reversal of 221100021 is 120001122.

It can be written as a sum of positive squares in only one way, i.e., 155975121 + 65124900 = 12489^2 + 8070^2 .

It is a de Polignac number, because none of the positive numbers 2^k-221100021 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (9), and also a Moran number because the ratio is a prime number: 24566669 = 221100021 / (2 + 2 + 1 + 1 + 0 + 0 + 0 + 2 + 1).

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 221099976 and 221100012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (221100041) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 12283326 + ... + 12283343.

It is an arithmetic number, because the mean of its divisors is an integer number (53227785).

Almost surely, 2^221100021 is an apocalyptic number.

It is an amenable number.

221100021 is a deficient number, since it is larger than the sum of its proper divisors (98266689).

221100021 is a wasteful number, since it uses less digits than its factorization.

221100021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24566675 (or 24566672 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 9.

The square root of 221100021 is about 14869.4324370502. The cubic root of 221100021 is about 604.6855556975.

Adding to 221100021 its reverse (120001122), we get a palindrome (341101143).

The spelling of 221100021 in words is "two hundred twenty-one million, one hundred thousand, twenty-one".