521 has 2 divisors, whose sum is σ = 522. Its totient is φ = 520.

The previous prime is 509. The next prime is 523. The reversal of 521 is 125.

Adding to 521 its reverse (125), we get a palindrome (646).

It can be divided in two parts, 5 and 21, that multiplied together give a triangular number (105 = T_{14}).

521 is nontrivially palindromic in base 11.

521 is an esthetic number in base 11, because in such base its adjacent digits differ by 1.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 400 + 121 = 20^2 + 11^2 .

It is a cyclic number.

It is not a de Polignac number, because 521 - 2^{6} = 457 is a prime.

Together with 523, it forms a pair of twin primes.

It is a Chen prime.

It is a Lucas number.

It is an alternating number because its digits alternate between odd and even.

521 is an undulating number in base 11.

It is a plaindrome in base 6 and base 15.

It is a nialpdrome in base 10 and base 13.

It is a junction number, because it is equal to *n*+sod(*n*) for *n* = 499 and 508.

It is an inconsummate number, since it does not exist a number *n* which divided by its sum of digits gives 521.

It is not a weakly prime, because it can be changed into another prime (523) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (3) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 260 + 261.

It is an arithmetic number, because the mean of its divisors is an integer number (261).

It is an amenable number.

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

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

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

The product of its digits is 10, while the sum is 8.

The square root of 521 is about 22.8254244210. The cubic root of 521 is about 8.0466029930.

The spelling of 521 in words is "five hundred twenty-one", and thus it is an aban number.

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