216660721 has 2 divisors, whose sum is σ = 216660722. Its totient is φ = 216660720.

The previous prime is 216660707. The next prime is 216660727. The reversal of 216660721 is 127066612.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 206324496 + 10336225 = 14364^2 + 3215^2 .

It is a cyclic number.

It is not a de Polignac number, because 216660721 - 2¹⁵ = 216627953 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (216660727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108330360 + 108330361.

It is an arithmetic number, because the mean of its divisors is an integer number (108330361).

Almost surely, 2^216660721 is an apocalyptic number.

It is an amenable number.

216660721 is a deficient number, since it is larger than the sum of its proper divisors (1).

216660721 is an equidigital number, since it uses as much as digits as its factorization.

216660721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6048, while the sum is 31.

The square root of 216660721 is about 14719.3994782396. The cubic root of 216660721 is about 600.6111559730.

The spelling of 216660721 in words is "two hundred sixteen million, six hundred sixty thousand, seven hundred twenty-one".