16678721 has 2 divisors, whose sum is σ = 16678722. Its totient is φ = 16678720.

The previous prime is 16678679. The next prime is 16678733. The reversal of 16678721 is 12787661.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11296321 + 5382400 = 3361^2 + 2320^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-16678721 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (16678771) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8339360 + 8339361.

It is an arithmetic number, because the mean of its divisors is an integer number (8339361).

Almost surely, 2^16678721 is an apocalyptic number.

It is an amenable number.

16678721 is a deficient number, since it is larger than the sum of its proper divisors (1).

16678721 is an equidigital number, since it uses as much as digits as its factorization.

16678721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 28224, while the sum is 38.

The square root of 16678721 is about 4083.9589860820. The cubic root of 16678721 is about 255.4980449527.

It can be divided in two parts, 166 and 78721, that added together give a palindrome (78887).

The spelling of 16678721 in words is "sixteen million, six hundred seventy-eight thousand, seven hundred twenty-one".