16638221 has 2 divisors, whose sum is σ = 16638222. Its totient is φ = 16638220.

The previous prime is 16638217. The next prime is 16638247. The reversal of 16638221 is 12283661.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11485321 + 5152900 = 3389^2 + 2270^2 .

It is a cyclic number.

It is not a de Polignac number, because 16638221 - 2² = 16638217 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (16637221) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8319110 + 8319111.

It is an arithmetic number, because the mean of its divisors is an integer number (8319111).

Almost surely, 2^16638221 is an apocalyptic number.

It is an amenable number.

16638221 is a deficient number, since it is larger than the sum of its proper divisors (1).

16638221 is an equidigital number, since it uses as much as digits as its factorization.

16638221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3456, while the sum is 29.

The square root of 16638221 is about 4078.9975484180. The cubic root of 16638221 is about 255.2910734930.

The spelling of 16638221 in words is "sixteen million, six hundred thirty-eight thousand, two hundred twenty-one".