20917 has 4 divisors (see below), whose sum is σ = 22540. Its totient is φ = 19296.

The previous prime is 20903. The next prime is 20921. The reversal of 20917 is 71902.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 71902 = 2 ⋅35951.

It can be written as a sum of positive squares in 2 ways, for example, as 12996 + 7921 = 114^2 + 89^2 .

It is a cyclic number.

It is not a de Polignac number, because 20917 - 2⁷ = 20789 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20894 and 20903.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20947) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 792 + ... + 817.

It is an arithmetic number, because the mean of its divisors is an integer number (5635).

2²⁰⁹¹⁷ is an apocalyptic number.

20917 is the 84-th hex number.

It is an amenable number.

20917 is a deficient number, since it is larger than the sum of its proper divisors (1623).

20917 is a wasteful number, since it uses less digits than its factorization.

20917 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1622.

The product of its (nonzero) digits is 126, while the sum is 19.

The square root of 20917 is about 144.6271067262. The cubic root of 20917 is about 27.5528460405.

It can be divided in two parts, 209 and 17, that multiplied together give a palindrome (3553).

The spelling of 20917 in words is "twenty thousand, nine hundred seventeen".