19778940721 has 4 divisors (see below), whose sum is σ = 20001176100. Its totient is φ = 19556705344.

The previous prime is 19778940707. The next prime is 19778940767. The reversal of 19778940721 is 12704987791.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 6538986496 + 13239954225 = 80864^2 + 115065^2 .

It is a cyclic number.

It is not a de Polignac number, because 19778940721 - 2¹⁹ = 19778416433 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (19778943721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 111117556 + ... + 111117733.

It is an arithmetic number, because the mean of its divisors is an integer number (5000294025).

Almost surely, 2^19778940721 is an apocalyptic number.

It is an amenable number.

19778940721 is a deficient number, since it is larger than the sum of its proper divisors (222235379).

19778940721 is an equidigital number, since it uses as much as digits as its factorization.

19778940721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 222235378.

The product of its (nonzero) digits is 1778112, while the sum is 55.

The spelling of 19778940721 in words is "nineteen billion, seven hundred seventy-eight million, nine hundred forty thousand, seven hundred twenty-one".