21598 has 4 divisors (see below), whose sum is σ = 32400. Its totient is φ = 10798.

The previous prime is 21589. The next prime is 21599. The reversal of 21598 is 89512.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21599) by changing a digit.

21598 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is an upside-down number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5398 + ... + 5401.

It is an arithmetic number, because the mean of its divisors is an integer number (8100).

2²¹⁵⁹⁸ is an apocalyptic number.

21598 is a deficient number, since it is larger than the sum of its proper divisors (10802).

21598 is a wasteful number, since it uses less digits than its factorization.

21598 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10801.

The product of its digits is 720, while the sum is 25.

The square root of 21598 is about 146.9625802713. The cubic root of 21598 is about 27.8486734217.

It can be divided in two parts, 215 and 98, that added together give a palindrome (313).

The spelling of 21598 in words is "twenty-one thousand, five hundred ninety-eight".