20566 has 16 divisors (see below), whose sum is σ = 38304. Its totient is φ = 8064.

The previous prime is 20563. The next prime is 20593. The reversal of 20566 is 66502.

20566 is an esthetic number in base 12, because in such base its adjacent digits differ by 1.

20566 is an undulating number in base 15.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20563) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 126 + ... + 238.

It is an arithmetic number, because the mean of its divisors is an integer number (2394).

2²⁰⁵⁶⁶ is an apocalyptic number.

20566 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

20566 is the 91-st heptagonal number.

20566 is a deficient number, since it is larger than the sum of its proper divisors (17738).

20566 is a wasteful number, since it uses less digits than its factorization.

20566 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 135.

The product of its (nonzero) digits is 360, while the sum is 19.

The square root of 20566 is about 143.4085074185. The cubic root of 20566 is about 27.3978580029.

It can be divided in two parts, 205 and 66, that multiplied together give a triangular number (13530 = T₁₆₄).

The spelling of 20566 in words is "twenty thousand, five hundred sixty-six".