218509021 has 2 divisors, whose sum is σ = 218509022. Its totient is φ = 218509020.

The previous prime is 218509019. The next prime is 218509069. The reversal of 218509021 is 120905812.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 171243396 + 47265625 = 13086^2 + 6875^2 .

It is a cyclic number.

It is not a de Polignac number, because 218509021 - 2¹ = 218509019 is a prime.

Together with 218509019, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (218509091) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 109254510 + 109254511.

It is an arithmetic number, because the mean of its divisors is an integer number (109254511).

Almost surely, 2^218509021 is an apocalyptic number.

It is an amenable number.

218509021 is a deficient number, since it is larger than the sum of its proper divisors (1).

218509021 is an equidigital number, since it uses as much as digits as its factorization.

218509021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1440, while the sum is 28.

The square root of 218509021 is about 14782.0506358218. The cubic root of 218509021 is about 602.3142300155.

The spelling of 218509021 in words is "two hundred eighteen million, five hundred nine thousand, twenty-one".