20721996788164 has 27 divisors (see below), whose sum is σ = 42184194626637. Its totient is φ = 8880828453504.

The previous prime is 20721996788161. The next prime is 20721996788239. The reversal of 20721996788164 is 46188769912702.

The square root of 20721996788164 is 4552142.

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

It can be written as a sum of positive squares in only one way, i.e., 15836977384900 + 4885019403264 = 3979570^2 + 2210208^2 .

It is a junction number, because it is equal to n+sod(n) for n = 20721996788093 and 20721996788102.

It is not an unprimeable number, because it can be changed into a prime (20721996788161) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 63567412 + ... + 63892564.

Almost surely, 2^{20721996788164} is an apocalyptic number.

20721996788164 is the 4552142-nd square number.

It is an amenable number.

20721996788164 is an abundant number, since it is smaller than the sum of its proper divisors (21462197838473).

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

20721996788164 is an frugal number, since it uses more digits than its factorization.

20721996788164 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 650324 (or 325162 counting only the distinct ones).

The product of its (nonzero) digits is 146313216, while the sum is 70.

The spelling of 20721996788164 in words is "twenty trillion, seven hundred twenty-one billion, nine hundred ninety-six million, seven hundred eighty-eight thousand, one hundred sixty-four".