218521 has 2 divisors, whose sum is σ = 218522. Its totient is φ = 218520.

The previous prime is 218513. The next prime is 218527. The reversal of 218521 is 125812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 112896 + 105625 = 336^2 + 325^2 .

It is a cyclic number.

It is not a de Polignac number, because 218521 - 2³ = 218513 is a prime.

It is an Ulam number.

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

218521 is a lucky number.

It is a plaindrome in base 16.

It is not a weakly prime, because it can be changed into another prime (218527) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 109260 + 109261.

It is an arithmetic number, because the mean of its divisors is an integer number (109261).

2²¹⁸⁵²¹ is an apocalyptic number.

It is an amenable number.

218521 is a deficient number, since it is larger than the sum of its proper divisors (1).

218521 is an equidigital number, since it uses as much as digits as its factorization.

218521 is an evil number, because the sum of its binary digits is even.

The product of its digits is 160, while the sum is 19.

The square root of 218521 is about 467.4622979450. The cubic root of 218521 is about 60.2325236411.

The spelling of 218521 in words is "two hundred eighteen thousand, five hundred twenty-one".