19781643 has 24 divisors (see below), whose sum is σ = 31519632. Its totient is φ = 10995264.

The previous prime is 19781623. The next prime is 19781681. The reversal of 19781643 is 34618791.

It is not a de Polignac number, because 19781643 - 2⁵ = 19781611 is a prime.

It is a hoax number, since the sum of its digits (39) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (19781623) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 3621 + ... + 7257.

It is an arithmetic number, because the mean of its divisors is an integer number (1313318).

Almost surely, 2^19781643 is an apocalyptic number.

19781643 is a deficient number, since it is larger than the sum of its proper divisors (11737989).

19781643 is a wasteful number, since it uses less digits than its factorization.

19781643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3691 (or 3684 counting only the distinct ones).

The product of its digits is 36288, while the sum is 39.

The square root of 19781643 is about 4447.6558994598. The cubic root of 19781643 is about 270.4502911358.

The spelling of 19781643 in words is "nineteen million, seven hundred eighty-one thousand, six hundred forty-three".