• Sorting the digits of 21091 in ascending order we obtain a prime of 308 digits.
1091 has 2 divisors, whose sum is σ = 1092. Its totient is φ = 1090.
The previous prime is 1087. The next prime is 1093. The reversal of 1091 is 1901.
1091 is nontrivially palindromic in base 5.
It is a strong prime.
It is an emirp because it is prime and its reverse (1901) is a distict prime. It is also a bemirp because it and its reverse can be mirrored producing other two distinct primes, 1601 and 1061.
It is a cyclic number.
It is not a de Polignac number, because 1091 - 22 = 1087 is a prime.
Together with 1093, it forms a pair of twin primes.
It is a Chen prime.
It is equal to p182 and since 1091 and 182 have the same sum of digits, it is a Honaker prime.
It is a plaindrome in base 14.
It is a nialpdrome in base 16.
It is not a weakly prime, because it can be changed into another prime (1093) by changing a digit.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 545 + 546.
It is an arithmetic number, because the mean of its divisors is an integer number (546).
1091 is a deficient number, since it is larger than the sum of its proper divisors (1).
1091 is an equidigital number, since it uses as much as digits as its factorization.
1091 is an evil number, because the sum of its binary digits is even.
The product of its (nonzero) digits is 9, while the sum is 11.
The square root of 1091 is about 33.0302891298. The cubic root of 1091 is about 10.2945709284.
Adding to 1091 its reverse (1901), we get a palindrome (2992).
It can be divided in two parts, 10 and 91, that added together give a palindrome (101).
The spelling of 1091 in words is "one thousand, ninety-one".
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