15685981 has 2 divisors, whose sum is σ = 15685982. Its totient is φ = 15685980.

The previous prime is 15685939. The next prime is 15685987. The reversal of 15685981 is 18958651.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15444900 + 241081 = 3930^2 + 491^2 .

It is an emirp because it is prime and its reverse (18958651) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 15685981 - 2¹¹ = 15683933 is a prime.

It is a super-2 number, since 2×15685981² = 492099999864722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (15685987) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 7842990 + 7842991.

It is an arithmetic number, because the mean of its divisors is an integer number (7842991).

Almost surely, 2^15685981 is an apocalyptic number.

It is an amenable number.

15685981 is a deficient number, since it is larger than the sum of its proper divisors (1).

15685981 is an equidigital number, since it uses as much as digits as its factorization.

15685981 is an evil number, because the sum of its binary digits is even.

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

The square root of 15685981 is about 3960.5531179369. The cubic root of 15685981 is about 250.3248098116.

The spelling of 15685981 in words is "fifteen million, six hundred eighty-five thousand, nine hundred eighty-one".