16815221 has 2 divisors, whose sum is σ = 16815222. Its totient is φ = 16815220.

The previous prime is 16815173. The next prime is 16815233. The reversal of 16815221 is 12251861.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11122225 + 5692996 = 3335^2 + 2386^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-16815221 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (16815251) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8407610 + 8407611.

It is an arithmetic number, because the mean of its divisors is an integer number (8407611).

Almost surely, 2^16815221 is an apocalyptic number.

It is an amenable number.

16815221 is a deficient number, since it is larger than the sum of its proper divisors (1).

16815221 is an equidigital number, since it uses as much as digits as its factorization.

16815221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 960, while the sum is 26.

The square root of 16815221 is about 4100.6366578862. The cubic root of 16815221 is about 256.1931576477.

The spelling of 16815221 in words is "sixteen million, eight hundred fifteen thousand, two hundred twenty-one".