216521 has 4 divisors (see below), whose sum is σ = 221844. Its totient is φ = 211200.

The previous prime is 216509. The next prime is 216523. The reversal of 216521 is 125612.

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 18496 + 198025 = 136^2 + 445^2 .

It is a cyclic number.

It is not a de Polignac number, because 216521 - 2^{10} = 215497 is a prime.

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

It is a Duffinian number.

It is a self number, because there is not a number *n* which added to its sum of digits gives 216521.

It is a congruent number.

It is an inconsummate number, since it does not exist a number *n* which divided by its sum of digits gives 216521.

It is not an unprimeable number, because it can be changed into a prime (216523) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2600 + ... + 2681.

It is an arithmetic number, because the mean of its divisors is an integer number (55461).

2^{216521} is an apocalyptic number.

It is an amenable number.

216521 is a deficient number, since it is larger than the sum of its proper divisors (5323).

216521 is an equidigital number, since it uses as much as digits as its factorization.

216521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5322.

The product of its digits is 120, while the sum is 17.

The square root of 216521 is about 465.3181707176. The cubic root of 216521 is about 60.0482020065.

Subtracting from 216521 its reverse (125612), we obtain a palindrome (90909).

It can be divided in two parts, 216 and 521, that added together give a palindrome (737).

The spelling of 216521 in words is "two hundred sixteen thousand, five hundred twenty-one".

• e-mail: info -at- numbersaplenty.com • Privacy notice • done in 0.026 sec. • engine limits •