21173023656 has 96 divisors (see below), whose sum is σ = 59468409000. Its totient is φ = 6797371392.

The previous prime is 21173023649. The next prime is 21173023687. The reversal of 21173023656 is 65632037112.

It can be written as a sum of positive squares in 4 ways, for example, as 20496503556 + 676520100 = 143166^2 + 26010^2 .

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a self number, because there is not a number n which added to its sum of digits gives 21173023656.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 841596 + ... + 866388.

Almost surely, 2^21173023656 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21173023656, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29734204500).

21173023656 is an abundant number, since it is smaller than the sum of its proper divisors (38295385344).

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

21173023656 is a wasteful number, since it uses less digits than its factorization.

21173023656 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 25243 (or 25236 counting only the distinct ones).

The product of its (nonzero) digits is 45360, while the sum is 36.

The spelling of 21173023656 in words is "twenty-one billion, one hundred seventy-three million, twenty-three thousand, six hundred fifty-six".