21655660 has 72 divisors (see below), whose sum is σ = 50727600. Its totient is φ = 7757568.

The previous prime is 21655657. The next prime is 21655679. The reversal of 21655660 is 6655612.

It is a super-2 number, since 2×21655660² = 937935220071200, which contains 22 as substring.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 145266 + ... + 145414.

It is an arithmetic number, because the mean of its divisors is an integer number (704550).

Almost surely, 2^21655660 is an apocalyptic number.

21655660 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 21655660, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25363800).

21655660 is an abundant number, since it is smaller than the sum of its proper divisors (29071940).

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

21655660 is a wasteful number, since it uses less digits than its factorization.

21655660 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 227 (or 212 counting only the distinct ones).

The product of its (nonzero) digits is 10800, while the sum is 31.

The square root of 21655660 is about 4653.5642254083. The cubic root of 21655660 is about 278.7343385733.

The spelling of 21655660 in words is "twenty-one million, six hundred fifty-five thousand, six hundred sixty".