19987681 has 4 divisors (see below), whose sum is σ = 22843072. Its totient is φ = 17132292.

The previous prime is 19987673. The next prime is 19987697. The reversal of 19987681 is 18678991.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 18678991 = 137 ⋅136343.

It is a cyclic number.

It is not a de Polignac number, because 19987681 - 2³ = 19987673 is a prime.

It is a super-2 number, since 2×19987681² = 799014783515522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (19987081) 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 in 3 ways as a sum of consecutive naturals, for example, 1427685 + ... + 1427698.

It is an arithmetic number, because the mean of its divisors is an integer number (5710768).

Almost surely, 2^19987681 is an apocalyptic number.

It is an amenable number.

19987681 is a deficient number, since it is larger than the sum of its proper divisors (2855391).

19987681 is an equidigital number, since it uses as much as digits as its factorization.

19987681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2855390.

The product of its digits is 217728, while the sum is 49.

The square root of 19987681 is about 4470.7584367756. The cubic root of 19987681 is about 271.3860186953.

The spelling of 19987681 in words is "nineteen million, nine hundred eighty-seven thousand, six hundred eighty-one".