20605 has 8 divisors (see below), whose sum is σ = 26712. Its totient is φ = 15168.

The previous prime is 20599. The next prime is 20611. The reversal of 20605 is 50602.

20605 = T₁₁ + T₁₂ + ... + T₄₉.

20605 = 101² + 102².

It is an interprime number because it is at equal distance from previous prime (20599) and next prime (20611).

It can be written as a sum of positive squares in 4 ways, for example, as 441 + 20164 = 21^2 + 142^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 20605 - 2⁷ = 20477 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (13).

It is a Duffinian number.

20605 is a lucky number.

It is a nialpdrome in base 12.

It is a zygodrome in base 12.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 94 + ... + 223.

It is an arithmetic number, because the mean of its divisors is an integer number (3339).

2²⁰⁶⁰⁵ is an apocalyptic number.

20605 is the 102-nd centered square number.

It is an amenable number.

20605 is a deficient number, since it is larger than the sum of its proper divisors (6107).

20605 is a wasteful number, since it uses less digits than its factorization.

20605 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 335.

The product of its (nonzero) digits is 60, while the sum is 13.

The square root of 20605 is about 143.5444182126. The cubic root of 20605 is about 27.4151655616.

It can be divided in two parts, 20 and 605, that multiplied together give a square (12100 = 110²).

The spelling of 20605 in words is "twenty thousand, six hundred five".