16640681 has 2 divisors, whose sum is σ = 16640682. Its totient is φ = 16640680.

The previous prime is 16640651. The next prime is 16640731. The reversal of 16640681 is 18604661.

16640681 = 2884² + 2885².

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 8323225 + 8317456 = 2885^2 + 2884^2 .

It is an emirp because it is prime and its reverse (18604661) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 16640681 - 2¹⁰ = 16639657 is a prime.

It is a super-2 number, since 2×16640681² = 553824528287522, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (16640621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8320340 + 8320341.

It is an arithmetic number, because the mean of its divisors is an integer number (8320341).

Almost surely, 2^16640681 is an apocalyptic number.

16640681 is the 2885-th centered square number.

It is an amenable number.

16640681 is a deficient number, since it is larger than the sum of its proper divisors (1).

16640681 is an equidigital number, since it uses as much as digits as its factorization.

16640681 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6912, while the sum is 32.

The square root of 16640681 is about 4079.2990819502. The cubic root of 16640681 is about 255.3036546676.

The spelling of 16640681 in words is "sixteen million, six hundred forty thousand, six hundred eighty-one".