21189901 has 4 divisors (see below), whose sum is σ = 21399804. Its totient is φ = 20980000.

The previous prime is 21189899. The next prime is 21189913. The reversal of 21189901 is 10998112.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 19624900 + 1565001 = 4430^2 + 1251^2 .

It is a cyclic number.

It is not a de Polignac number, because 21189901 - 2¹ = 21189899 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 (21189101) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 104800 + ... + 105001.

It is an arithmetic number, because the mean of its divisors is an integer number (5349951).

Almost surely, 2^21189901 is an apocalyptic number.

It is an amenable number.

21189901 is a deficient number, since it is larger than the sum of its proper divisors (209903).

21189901 is a wasteful number, since it uses less digits than its factorization.

21189901 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 209902.

The product of its (nonzero) digits is 1296, while the sum is 31.

The square root of 21189901 is about 4603.2489613316. The cubic root of 21189901 is about 276.7215463463.

The spelling of 21189901 in words is "twenty-one million, one hundred eighty-nine thousand, nine hundred one".