21991056821054 has 16 divisors (see below), whose sum is σ = 33538037218416. Its totient is φ = 10811826009600.

The previous prime is 21991056821051. The next prime is 21991056821081. The reversal of 21991056821054 is 45012865019912.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21991056820987 and 21991056821005.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21991056821051) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 28347692 + ... + 29113119.

It is an arithmetic number, because the mean of its divisors is an integer number (2096127326151).

Almost surely, 2^{21991056821054} is an apocalyptic number.

21991056821054 is a deficient number, since it is larger than the sum of its proper divisors (11546980397362).

21991056821054 is a wasteful number, since it uses less digits than its factorization.

21991056821054 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 57464011.

The product of its (nonzero) digits is 1555200, while the sum is 53.

The spelling of 21991056821054 in words is "twenty-one trillion, nine hundred ninety-one billion, fifty-six million, eight hundred twenty-one thousand, fifty-four".