19869809779721 has 4 divisors (see below), whose sum is σ = 21676156123344. Its totient is φ = 18063463436100.

The previous prime is 19869809779709. The next prime is 19869809779723. The reversal of 19869809779721 is 12797790896891.

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.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-19869809779721 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 19869809779721.

It is not an unprimeable number, because it can be changed into a prime (19869809779723) 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, 903173171795 + ... + 903173171816.

It is an arithmetic number, because the mean of its divisors is an integer number (5419039030836).

Almost surely, 2^{19869809779721} is an apocalyptic number.

19869809779721 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

19869809779721 is a deficient number, since it is larger than the sum of its proper divisors (1806346343623).

19869809779721 is a wasteful number, since it uses less digits than its factorization.

19869809779721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1806346343622.

The product of its (nonzero) digits is 1728324864, while the sum is 83.

The spelling of 19869809779721 in words is "nineteen trillion, eight hundred sixty-nine billion, eight hundred nine million, seven hundred seventy-nine thousand, seven hundred twenty-one".