20957 has 4 divisors (see below), whose sum is σ = 22080. Its totient is φ = 19836.
The previous prime is 20947. The next prime is 20959. The reversal of 20957 is 75902.
It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 75902 = 2 ⋅37951.
It is a de Polignac number, because none of the positive numbers 2k-20957 is a prime.
It is a Duffinian number.
It is a plaindrome in base 14.
It is a nialpdrome in base 15.
It is a congruent number.
It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 20957.
It is not an unprimeable number, because it can be changed into a prime (20959) 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, 533 + ... + 570.
It is an arithmetic number, because the mean of its divisors is an integer number (5520).
220957 is an apocalyptic number.
It is an amenable number.
20957 is a deficient number, since it is larger than the sum of its proper divisors (1123).
20957 is a wasteful number, since it uses less digits than its factorization.
20957 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 1122.
The product of its (nonzero) digits is 630, while the sum is 23.
The square root of 20957 is about 144.7653273405. The cubic root of 20957 is about 27.5703981441.
Subtracting 20957 from its reverse (75902), we obtain a palindrome (54945).
The spelling of 20957 in words is "twenty thousand, nine hundred fifty-seven".
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