20991776955864 has 128 divisors (see below), whose sum is σ = 61663954060800. Its totient is φ = 5870893916160.

The previous prime is 20991776955829. The next prime is 20991776955887. The reversal of 20991776955864 is 46855967719902.

It is a Harshad number since it is a multiple of its sum of digits (78).

It is a self number, because there is not a number n which added to its sum of digits gives 20991776955864.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 21287032 + ... + 22251320.

It is an arithmetic number, because the mean of its divisors is an integer number (481749641100).

Almost surely, 2^{20991776955864} is an apocalyptic number.

20991776955864 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 20991776955864, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30831977030400).

20991776955864 is an abundant number, since it is smaller than the sum of its proper divisors (40672177104936).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

20991776955864 is a wasteful number, since it uses less digits than its factorization.

20991776955864 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 970665 (or 970661 counting only the distinct ones).

The product of its (nonzero) digits is 2057529600, while the sum is 78.

The spelling of 20991776955864 in words is "twenty trillion, nine hundred ninety-one billion, seven hundred seventy-six million, nine hundred fifty-five thousand, eight hundred sixty-four".