218970821 has 2 divisors, whose sum is σ = 218970822. Its totient is φ = 218970820.

The previous prime is 218970809. The next prime is 218970827. The reversal of 218970821 is 128079812.

218970821 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 215766721 + 3204100 = 14689^2 + 1790^2 .

It is a cyclic number.

It is not a de Polignac number, because 218970821 - 2²² = 214776517 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (218970827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 109485410 + 109485411.

It is an arithmetic number, because the mean of its divisors is an integer number (109485411).

Almost surely, 2^218970821 is an apocalyptic number.

It is an amenable number.

218970821 is a deficient number, since it is larger than the sum of its proper divisors (1).

218970821 is an equidigital number, since it uses as much as digits as its factorization.

218970821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 16128, while the sum is 38.

The square root of 218970821 is about 14797.6626870597. The cubic root of 218970821 is about 602.7382445361.

The spelling of 218970821 in words is "two hundred eighteen million, nine hundred seventy thousand, eight hundred twenty-one".