15985681 has 2 divisors, whose sum is σ = 15985682. Its totient is φ = 15985680.

The previous prime is 15985679. The next prime is 15985709. The reversal of 15985681 is 18658951.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15928081 + 57600 = 3991^2 + 240^2 .

It is a cyclic number.

It is not a de Polignac number, because 15985681 - 2¹ = 15985679 is a prime.

It is a super-2 number, since 2×15985681² = 511083994067522, which contains 22 as substring.

Together with 15985679, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (15985381) 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, 7992840 + 7992841.

It is an arithmetic number, because the mean of its divisors is an integer number (7992841).

Almost surely, 2^15985681 is an apocalyptic number.

It is an amenable number.

15985681 is a deficient number, since it is larger than the sum of its proper divisors (1).

15985681 is an equidigital number, since it uses as much as digits as its factorization.

15985681 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 86400, while the sum is 43.

The square root of 15985681 is about 3998.2097243641. The cubic root of 15985681 is about 251.9090175040.

Adding to 15985681 its product of digits (86400), we get a square (16072081 = 4009²).

The spelling of 15985681 in words is "fifteen million, nine hundred eighty-five thousand, six hundred eighty-one".