20399 has 2 divisors, whose sum is σ = 20400. Its totient is φ = 20398.

The previous prime is 20393. The next prime is 20407. The reversal of 20399 is 99302.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 20399 - 2⁸ = 20143 is a prime.

It is a super-2 number, since 2×20399² = 832238402, which contains 22 as substring.

It is a Chen prime.

It is an Ulam number.

It is a nialpdrome in base 14.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20393) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10199 + 10200.

It is an arithmetic number, because the mean of its divisors is an integer number (10200).

2²⁰³⁹⁹ is an apocalyptic number.

20399 is a deficient number, since it is larger than the sum of its proper divisors (1).

20399 is an equidigital number, since it uses as much as digits as its factorization.

20399 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 486, while the sum is 23.

The square root of 20399 is about 142.8250678277. The cubic root of 20399 is about 27.3234976840.

It can be divided in two parts, 2039 and 9, that added together give a 11-th power (2048 = 2¹¹).

The spelling of 20399 in words is "twenty thousand, three hundred ninety-nine".