16909721 has 2 divisors, whose sum is σ = 16909722. Its totient is φ = 16909720.

The previous prime is 16909699. The next prime is 16909727. The reversal of 16909721 is 12790961.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11316496 + 5593225 = 3364^2 + 2365^2 .

It is an emirp because it is prime and its reverse (12790961) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-16909721 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (16909727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8454860 + 8454861.

It is an arithmetic number, because the mean of its divisors is an integer number (8454861).

Almost surely, 2^16909721 is an apocalyptic number.

It is an amenable number.

16909721 is a deficient number, since it is larger than the sum of its proper divisors (1).

16909721 is an equidigital number, since it uses as much as digits as its factorization.

16909721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6804, while the sum is 35.

The square root of 16909721 is about 4112.1431152138. The cubic root of 16909721 is about 256.6721887457.

It can be divided in two parts, 1690 and 9721, that added together give a palindrome (11411).

The spelling of 16909721 in words is "sixteen million, nine hundred nine thousand, seven hundred twenty-one".