21506216656 has 80 divisors (see below), whose sum is σ = 44429299200. Its totient is φ = 10049808384.

The previous prime is 21506216621. The next prime is 21506216657. The reversal of 21506216656 is 65661260512.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21506216657) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 46449481 + ... + 46449943.

It is an arithmetic number, because the mean of its divisors is an integer number (555366240).

Almost surely, 2^21506216656 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 21506216656, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22214649600).

21506216656 is an abundant number, since it is smaller than the sum of its proper divisors (22923082544).

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

21506216656 is a wasteful number, since it uses less digits than its factorization.

21506216656 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1316 (or 1310 counting only the distinct ones).

The product of its (nonzero) digits is 129600, while the sum is 40.

The spelling of 21506216656 in words is "twenty-one billion, five hundred six million, two hundred sixteen thousand, six hundred fifty-six".