16647721 has 2 divisors, whose sum is σ = 16647722. Its totient is φ = 16647720.

The previous prime is 16647707. The next prime is 16647733. The reversal of 16647721 is 12774661.

It is a happy number.

16647721 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., 15492096 + 1155625 = 3936^2 + 1075^2 .

It is an emirp because it is prime and its reverse (12774661) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 16647721 - 2⁷ = 16647593 is a prime.

It is a super-2 number, since 2×16647721² = 554293228987682, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (16647221) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8323860 + 8323861.

It is an arithmetic number, because the mean of its divisors is an integer number (8323861).

Almost surely, 2^16647721 is an apocalyptic number.

It is an amenable number.

16647721 is a deficient number, since it is larger than the sum of its proper divisors (1).

16647721 is an equidigital number, since it uses as much as digits as its factorization.

16647721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 14112, while the sum is 34.

The square root of 16647721 is about 4080.1618840433. The cubic root of 16647721 is about 255.3396524798.

The spelling of 16647721 in words is "sixteen million, six hundred forty-seven thousand, seven hundred twenty-one".