20961 has 12 divisors (see below), whose sum is σ = 32292. Its totient is φ = 13056.

The previous prime is 20959. The next prime is 20963. The reversal of 20961 is 16902.

It is an interprime number because it is at equal distance from previous prime (20959) and next prime (20963).

It can be written as a sum of positive squares in 2 ways, for example, as 14400 + 6561 = 120^2 + 81^2 .

It is not a de Polignac number, because 20961 - 2¹ = 20959 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20963) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 85 + ... + 221.

It is an arithmetic number, because the mean of its divisors is an integer number (2691).

2²⁰⁹⁶¹ is an apocalyptic number.

It is an amenable number.

20961 is a deficient number, since it is larger than the sum of its proper divisors (11331).

20961 is a wasteful number, since it uses less digits than its factorization.

20961 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 160 (or 157 counting only the distinct ones).

The product of its (nonzero) digits is 108, while the sum is 18.

The square root of 20961 is about 144.7791421442. The cubic root of 20961 is about 27.5721521257.

The spelling of 20961 in words is "twenty thousand, nine hundred sixty-one".