21901 has 6 divisors (see below), whose sum is σ = 24206. Its totient is φ = 19800.

The previous prime is 21893. The next prime is 21911. The reversal of 21901 is 10912.

It can be written as a sum of positive squares in only one way, i.e., 12100 + 9801 = 110^2 + 99^2 .

It is not a de Polignac number, because 21901 - 2³ = 21893 is a prime.

It is a Duffinian number.

It is a plaindrome in base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21911) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 31 + ... + 211.

2²¹⁹⁰¹ is an apocalyptic number.

21901 is the 121-st pentagonal number.

It is an amenable number.

21901 is a deficient number, since it is larger than the sum of its proper divisors (2305).

21901 is a wasteful number, since it uses less digits than its factorization.

21901 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 203 (or 192 counting only the distinct ones).

The product of its (nonzero) digits is 18, while the sum is 13.

The square root of 21901 is about 147.9898645178. The cubic root of 21901 is about 27.9782995126.

The spelling of 21901 in words is "twenty-one thousand, nine hundred one".