21605506500 has 96 divisors (see below), whose sum is σ = 63622540800. Its totient is φ = 5696697600.

The previous prime is 21605506463. The next prime is 21605506511. The reversal of 21605506500 is 560550612.

It is a super-2 number, since 2×21605506500² (a number of 21 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 52581 + ... + 214419.

It is an arithmetic number, because the mean of its divisors is an integer number (662734800).

Almost surely, 2^21605506500 is an apocalyptic number.

21605506500 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21605506500, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31811270400).

21605506500 is an abundant number, since it is smaller than the sum of its proper divisors (42017034300).

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

21605506500 is a wasteful number, since it uses less digits than its factorization.

21605506500 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 161950 (or 161938 counting only the distinct ones).

The product of its (nonzero) digits is 9000, while the sum is 30.

The spelling of 21605506500 in words is "twenty-one billion, six hundred five million, five hundred six thousand, five hundred".