21216665660 has 24 divisors (see below), whose sum is σ = 44558107776. Its totient is φ = 8486073920.

The previous prime is 21216665623. The next prime is 21216665663. The reversal of 21216665660 is 6656661212.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21216665663) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 361109 + ... + 415731.

It is an arithmetic number, because the mean of its divisors is an integer number (1856587824).

Almost surely, 2^21216665660 is an apocalyptic number.

21216665660 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21216665660 is an abundant number, since it is smaller than the sum of its proper divisors (23341442116).

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

21216665660 is a wasteful number, since it uses less digits than its factorization.

21216665660 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 74053 (or 74051 counting only the distinct ones).

The product of its (nonzero) digits is 155520, while the sum is 41.

The spelling of 21216665660 in words is "twenty-one billion, two hundred sixteen million, six hundred sixty-five thousand, six hundred sixty".