218400821 has 2 divisors, whose sum is σ = 218400822. Its totient is φ = 218400820.

The previous prime is 218400811. The next prime is 218400851. The reversal of 218400821 is 128004812.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 214036900 + 4363921 = 14630^2 + 2089^2 .

It is a cyclic number.

It is not a de Polignac number, because 218400821 - 2¹⁴ = 218384437 is a prime.

It is a super-2 number, since 2×218400821² = 95397837226948082, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (218400811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 109200410 + 109200411.

It is an arithmetic number, because the mean of its divisors is an integer number (109200411).

Almost surely, 2^218400821 is an apocalyptic number.

It is an amenable number.

218400821 is a deficient number, since it is larger than the sum of its proper divisors (1).

218400821 is an equidigital number, since it uses as much as digits as its factorization.

218400821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1024, while the sum is 26.

The square root of 218400821 is about 14778.3903385991. The cubic root of 218400821 is about 602.2147968064.

The spelling of 218400821 in words is "two hundred eighteen million, four hundred thousand, eight hundred twenty-one".