21120816956121 has 27 divisors (see below), whose sum is σ = 32198431478421. Its totient is φ = 13339297894104.

The previous prime is 21120816956087. The next prime is 21120816956149. The reversal of 21120816956121 is 12165961802112.

The square root of 21120816956121 is 4595739.

It is a perfect power (a square), and thus also a powerful number.

21120816956121 is a `hidden beast` number, since 2 + 1 + 1 + 2 + 0 + 8 + 1 + 69 + 561 + 21 = 666.

It is not a de Polignac number, because 21120816956121 - 2²³ = 21120808567513 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21120816956521) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 261916810 + ... + 261997436.

Almost surely, 2^{21120816956121} is an apocalyptic number.

21120816956121 is the 4595739-th square number.

21120816956121 is the 2297870-th centered octagonal number.

It is an amenable number.

21120816956121 is a deficient number, since it is larger than the sum of its proper divisors (11077614522300).

21120816956121 is an frugal number, since it uses more digits than its factorization.

21120816956121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 161298 (or 80649 counting only the distinct ones).

The product of its (nonzero) digits is 103680, while the sum is 45.

It can be divided in two parts, 211208169 and 56121, that added together give a triangular number (211264290 = T₂₀₅₅₅).

The spelling of 21120816956121 in words is "twenty-one trillion, one hundred twenty billion, eight hundred sixteen million, nine hundred fifty-six thousand, one hundred twenty-one".