20639 has 2 divisors, whose sum is σ = 20640. Its totient is φ = 20638.

The previous prime is 20627. The next prime is 20641. The reversal of 20639 is 93602.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20639 is a prime.

Together with 20641, it forms a pair of twin primes.

It is a Chen prime.

It is a nialpdrome in base 14.

It is a self number, because there is not a number n which added to its sum of digits gives 20639.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20939) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10319 + 10320.

It is an arithmetic number, because the mean of its divisors is an integer number (10320).

2²⁰⁶³⁹ is an apocalyptic number.

20639 is a deficient number, since it is larger than the sum of its proper divisors (1).

20639 is an equidigital number, since it uses as much as digits as its factorization.

20639 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 324, while the sum is 20.

The square root of 20639 is about 143.6627996386. The cubic root of 20639 is about 27.4302363924.

The spelling of 20639 in words is "twenty thousand, six hundred thirty-nine".