20521 has 2 divisors, whose sum is σ = 20522. Its totient is φ = 20520.

The previous prime is 20509. The next prime is 20533. The reversal of 20521 is 12502.

It is a balanced prime because it is at equal distance from previous prime (20509) and next prime (20533).

It can be written as a sum of positive squares in only one way, i.e., 18496 + 2025 = 136^2 + 45^2 .

It is a cyclic number.

It is not a de Polignac number, because 20521 - 2⁷ = 20393 is a prime.

It is a super-2 number, since 2×20521² = 842222882, which contains 22 as substring.

It is a Chen prime.

It is an Ulam number.

It is a plaindrome in base 11.

It is a nialpdrome in base 12.

It is a junction number, because it is equal to n+sod(n) for n = 20498 and 20507.

It is not a weakly prime, because it can be changed into another prime (20551) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10260 + 10261.

It is an arithmetic number, because the mean of its divisors is an integer number (10261).

2²⁰⁵²¹ is an apocalyptic number.

It is an amenable number.

20521 is a deficient number, since it is larger than the sum of its proper divisors (1).

20521 is an equidigital number, since it uses as much as digits as its factorization.

20521 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 20, while the sum is 10.

The square root of 20521 is about 143.2515270425. The cubic root of 20521 is about 27.3778605325.

The spelling of 20521 in words is "twenty thousand, five hundred twenty-one".