215685221 has 2 divisors, whose sum is σ = 215685222. Its totient is φ = 215685220.

The previous prime is 215685163. The next prime is 215685251. The reversal of 215685221 is 122586512.

215685221 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., 199120321 + 16564900 = 14111^2 + 4070^2 .

It is a cyclic number.

It is not a de Polignac number, because 215685221 - 2⁶ = 215685157 is a prime.

It is a super-2 number, since 2×215685221² = 93040229115637682, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (215685251) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 107842610 + 107842611.

It is an arithmetic number, because the mean of its divisors is an integer number (107842611).

Almost surely, 2^215685221 is an apocalyptic number.

It is an amenable number.

215685221 is a deficient number, since it is larger than the sum of its proper divisors (1).

215685221 is an equidigital number, since it uses as much as digits as its factorization.

215685221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 9600, while the sum is 32.

The square root of 215685221 is about 14686.2255532182. The cubic root of 215685221 is about 599.7083962647.

The spelling of 215685221 in words is "two hundred fifteen million, six hundred eighty-five thousand, two hundred twenty-one".