21545 has 8 divisors (see below), whose sum is σ = 26880. Its totient is φ = 16560.

The previous prime is 21529. The next prime is 21557. The reversal of 21545 is 54512.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21545 - 2⁴ = 21529 is a prime.

It is a plaindrome in base 14.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 86 + ... + 224.

It is an arithmetic number, because the mean of its divisors is an integer number (3360).

2²¹⁵⁴⁵ is an apocalyptic number.

It is an amenable number.

21545 is a deficient number, since it is larger than the sum of its proper divisors (5335).

21545 is a wasteful number, since it uses less digits than its factorization.

21545 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 175.

The product of its digits is 200, while the sum is 17.

The square root of 21545 is about 146.7821515035. The cubic root of 21545 is about 27.8258751895.

Subtracting from 21545 its sum of digits (17), we obtain a triangular number (21528 = T₂₀₇).

The spelling of 21545 in words is "twenty-one thousand, five hundred forty-five".