21658 has 24 divisors (see below), whose sum is σ = 43092. Its totient is φ = 8064.

The previous prime is 21649. The next prime is 21661. The reversal of 21658 is 85612.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 21609 + 49 = 147^2 + 7^2 .

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

It is a congruent number.

It is an unprimeable number.

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 in 11 ways as a sum of consecutive naturals, for example, 1266 + ... + 1282.

2²¹⁶⁵⁸ is an apocalyptic number.

21658 is a deficient number, since it is larger than the sum of its proper divisors (21434).

21658 is a wasteful number, since it uses less digits than its factorization.

21658 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 46 (or 39 counting only the distinct ones).

The product of its digits is 480, while the sum is 22.

The square root of 21658 is about 147.1665722914. The cubic root of 21658 is about 27.8744377748.

The spelling of 21658 in words is "twenty-one thousand, six hundred fifty-eight".