16399681 has 2 divisors, whose sum is σ = 16399682. Its totient is φ = 16399680.

The previous prime is 16399661. The next prime is 16399729. The reversal of 16399681 is 18699361.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11669056 + 4730625 = 3416^2 + 2175^2 .

It is an emirp because it is prime and its reverse (18699361) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 16399681 - 2¹³ = 16391489 is a prime.

It is a super-2 number, since 2×16399681² = 537899073803522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (16399601) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8199840 + 8199841.

It is an arithmetic number, because the mean of its divisors is an integer number (8199841).

Almost surely, 2^16399681 is an apocalyptic number.

It is an amenable number.

16399681 is a deficient number, since it is larger than the sum of its proper divisors (1).

16399681 is an equidigital number, since it uses as much as digits as its factorization.

16399681 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 69984, while the sum is 43.

The square root of 16399681 is about 4049.6519603541. The cubic root of 16399681 is about 254.0651712407.

The spelling of 16399681 in words is "sixteen million, three hundred ninety-nine thousand, six hundred eighty-one".