21673 has 2 divisors, whose sum is σ = 21674. Its totient is φ = 21672.

The previous prime is 21661. The next prime is 21683. The reversal of 21673 is 37612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21609 + 64 = 147^2 + 8^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21673 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21673.

It is not a weakly prime, because it can be changed into another prime (21613) 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, 10836 + 10837.

It is an arithmetic number, because the mean of its divisors is an integer number (10837).

2²¹⁶⁷³ is an apocalyptic number.

It is an amenable number.

21673 is a deficient number, since it is larger than the sum of its proper divisors (1).

21673 is an equidigital number, since it uses as much as digits as its factorization.

21673 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 252, while the sum is 19.

The square root of 21673 is about 147.2175261306. The cubic root of 21673 is about 27.8808714264.

It can be divided in two parts, 216 and 73, that added together give a square (289 = 17²).

The spelling of 21673 in words is "twenty-one thousand, six hundred seventy-three".