505 has 4 divisors (see below), whose sum is σ = 612. Its totient is φ = 400.

The previous prime is 503. The next prime is 509.

505 = 2^{2} + 3^{2} + ... + 11^{2}.

505 is nontrivially palindromic in base 10.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 361 + 144 = 19^2 + 12^2 .

It is not a de Polignac number, because 505 - 2^{1} = 503 is a prime.

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

It is a Duffinian number.

505 is an undulating number in base 10.

It is a plaindrome in base 15.

It is a nialpdrome in base 8 and base 9.

It is a junction number, because it is equal to *n*+sod(*n*) for *n* = 491 and 500.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (503) 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 3 ways as a sum of consecutive naturals, for example, 46 + ... + 55.

It is an arithmetic number, because the mean of its divisors is an integer number (153).

It is the magic constant of a 10 × 10 magic square.

It is an amenable number.

505 is a deficient number, since it is larger than the sum of its proper divisors (107).

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

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

The sum of its prime factors is 106.

The product of its (nonzero) digits is 25, while the sum is 10.

The square root of 505 is about 22.4722050542. The cubic root of 505 is about 7.9633742418.

Adding to 505 its sum of digits (10), we get a palindrome (515).

Multiplying 505 by its sum of digits (10), we get a triangular number (5050 = T_{100}).

It can be divided in two parts, 50 and 5, that added together give a palindrome (55).

The spelling of 505 in words is "five hundred five", and thus it is an aban number and an oban number.

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