16917721 has 2 divisors, whose sum is σ = 16917722. Its totient is φ = 16917720.

The previous prime is 16917709. The next prime is 16917739. The reversal of 16917721 is 12771961.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12355225 + 4562496 = 3515^2 + 2136^2 .

It is an emirp because it is prime and its reverse (12771961) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 16917721 - 2⁵ = 16917689 is a prime.

It is not a weakly prime, because it can be changed into another prime (16917421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8458860 + 8458861.

It is an arithmetic number, because the mean of its divisors is an integer number (8458861).

Almost surely, 2^16917721 is an apocalyptic number.

It is an amenable number.

16917721 is a deficient number, since it is larger than the sum of its proper divisors (1).

16917721 is an equidigital number, since it uses as much as digits as its factorization.

16917721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5292, while the sum is 34.

The square root of 16917721 is about 4113.1157289821. The cubic root of 16917721 is about 256.7126596239.

Subtracting from 16917721 its reverse (12771961), we obtain a triangular number (4145760 = T₂₈₇₉).

The spelling of 16917721 in words is "sixteen million, nine hundred seventeen thousand, seven hundred twenty-one".