21781958779 has 32 divisors (see below), whose sum is σ = 25624166400. Its totient is φ = 18507535200.

The previous prime is 21781958773. The next prime is 21781958789. The reversal of 21781958779 is 97785918712.

It is not a de Polignac number, because 21781958779 - 2¹⁷ = 21781827707 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21781958779.

It is not an unprimeable number, because it can be changed into a prime (21781958773) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 32952709 + ... + 32953369.

It is an arithmetic number, because the mean of its divisors is an integer number (800755200).

Almost surely, 2^21781958779 is an apocalyptic number.

21781958779 is a deficient number, since it is larger than the sum of its proper divisors (3842207621).

21781958779 is an equidigital number, since it uses as much as digits as its factorization.

21781958779 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1376 (or 1362 counting only the distinct ones).

The product of its digits is 17781120, while the sum is 64.

The spelling of 21781958779 in words is "twenty-one billion, seven hundred eighty-one million, nine hundred fifty-eight thousand, seven hundred seventy-nine".