19681643 has 4 divisors (see below), whose sum is σ = 19704720. Its totient is φ = 19658568.

The previous prime is 19681639. The next prime is 19681661. The reversal of 19681643 is 34618691.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 34618691 = 2417 ⋅14323.

It is a cyclic number.

It is not a de Polignac number, because 19681643 - 2² = 19681639 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 19681597 and 19681606.

It is not an unprimeable number, because it can be changed into a prime (19681693) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 10208 + ... + 11981.

It is an arithmetic number, because the mean of its divisors is an integer number (4926180).

Almost surely, 2^19681643 is an apocalyptic number.

19681643 is a deficient number, since it is larger than the sum of its proper divisors (23077).

19681643 is an equidigital number, since it uses as much as digits as its factorization.

19681643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23076.

The product of its digits is 31104, while the sum is 38.

The square root of 19681643 is about 4436.3997791002. The cubic root of 19681643 is about 269.9937950106.

The spelling of 19681643 in words is "nineteen million, six hundred eighty-one thousand, six hundred forty-three".