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815 = 5163

815 has 4 divisors (see below), whose sum is σ = 984. Its totient is φ = 648.

The previous prime is 811. The next prime is 821. The reversal of 815 is 518.

815 = T2 + T3 + ... + T16.

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

It is a cyclic number.

It is not a de Polignac number, because 815 - 22 = 811 is a prime.

It is a Duffinian number.

It is a plaindrome in base 8 and base 12.

It is a self number, because there is not a number n which added to its sum of digits gives 815.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (811) 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, 77 + ... + 86.

It is an arithmetic number, because the mean of its divisors is an integer number (246).

815 is a deficient number, since it is larger than the sum of its proper divisors (169).

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

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

The sum of its prime factors is 168.

The product of its digits is 40, while the sum is 14.

The square root of 815 is about 28.5482048472. The cubic root of 815 is about 9.3408386343.

It can be divided in two parts, 8 and 15, that multiplied together give a triangular number (120 = T15).

The spelling of 815 in words is "eight hundred fifteen", and thus it is an aban number and an oban number.

Divisors: 1 5 163 815