21898 has 4 divisors (see below), whose sum is σ = 32850. Its totient is φ = 10948.

The previous prime is 21893. The next prime is 21911. The reversal of 21898 is 89812.

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

It can be written as a sum of positive squares in only one way, i.e., 21609 + 289 = 147^2 + 17^2 .

It is an alternating number because its digits alternate between even and odd.

It is a plaindrome in base 16.

It is not an unprimeable number, because it can be changed into a prime (21893) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5473 + ... + 5476.

2²¹⁸⁹⁸ is an apocalyptic number.

21898 is a deficient number, since it is larger than the sum of its proper divisors (10952).

21898 is a wasteful number, since it uses less digits than its factorization.

21898 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10951.

The product of its digits is 1152, while the sum is 28.

The square root of 21898 is about 147.9797283414. The cubic root of 21898 is about 27.9770219647.

It can be divided in two parts, 2189 and 8, that added together give a cube (2197 = 13³).

The spelling of 21898 in words is "twenty-one thousand, eight hundred ninety-eight".