71821 has 2 divisors, whose sum is σ = 71822.
Its totient is φ = 71820.
The previous prime is 71809. The next prime is 71837. The reversal of 71821 is 12817.
71821 = 1892 + 1902.
It is a weak prime.
It can be written as a sum of positive squares in only one way, i.e., 36100 + 35721 = 190^2 + 189^2
It is a cyclic number.
It is not a de Polignac number, because 71821 - 25 = 71789 is a prime.
It is an Ulam number.
71821 is a lucky number.
It is a plaindrome in base 16.
It is a congruent number.
It is not a weakly prime, because it can be changed into another prime (71861) 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 as a sum of consecutive naturals, namely, 35910 + 35911.
It is an arithmetic number, because the mean of its divisors is an integer number (35911).
271821 is an apocalyptic number.
71821 is the 190-th centered square number.
It is an amenable number.
71821 is a deficient number, since it is larger than the sum of its proper divisors (1).
71821 is an equidigital number, since it uses as much as digits as its factorization.
71821 is an odious number, because the sum of its binary digits is odd.
The product of its digits is 112, while the sum is 19.
The square root of 71821 is about 267.9944029266.
The cubic root of 71821 is about 41.5671723882.
The spelling of 71821 in words is "seventy-one thousand, eight hundred twenty-one".