21021565660 has 48 divisors (see below), whose sum is σ = 45279999072. Its totient is φ = 8193427200.

The previous prime is 21021565627. The next prime is 21021565673. The reversal of 21021565660 is 6656512012.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 333030 + ... + 391090.

It is an arithmetic number, because the mean of its divisors is an integer number (943333314).

Almost surely, 2^21021565660 is an apocalyptic number.

21021565660 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 21021565660, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22639999536).

21021565660 is an abundant number, since it is smaller than the sum of its proper divisors (24258433412).

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

21021565660 is a wasteful number, since it uses less digits than its factorization.

21021565660 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 58534 (or 58532 counting only the distinct ones).

The product of its (nonzero) digits is 21600, while the sum is 34.

It can be divided in two parts, 21021565 and 660, that added together give a square (21022225 = 4585²).

The spelling of 21021565660 in words is "twenty-one billion, twenty-one million, five hundred sixty-five thousand, six hundred sixty".