21799 has 2 divisors, whose sum is σ = 21800. Its totient is φ = 21798.

The previous prime is 21787. The next prime is 21803. The reversal of 21799 is 99712.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21799 - 2⁵ = 21767 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21739) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10899 + 10900.

It is an arithmetic number, because the mean of its divisors is an integer number (10900).

2²¹⁷⁹⁹ is an apocalyptic number.

21799 is a deficient number, since it is larger than the sum of its proper divisors (1).

21799 is an equidigital number, since it uses as much as digits as its factorization.

21799 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1134, while the sum is 28.

The square root of 21799 is about 147.6448441362. The cubic root of 21799 is about 27.9347972618.

It can be divided in two parts, 21 and 799, that added together give a triangular number (820 = T₄₀).

The spelling of 21799 in words is "twenty-one thousand, seven hundred ninety-nine".