21655788 has 96 divisors (see below), whose sum is σ = 65802240. Its totient is φ = 5375040.

The previous prime is 21655787. The next prime is 21655813. The reversal of 21655788 is 88755612.

It is a Harshad number since it is a multiple of its sum of digits (42).

It is not an unprimeable number, because it can be changed into a prime (21655787) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 20743 + ... + 21761.

It is an arithmetic number, because the mean of its divisors is an integer number (685440).

Almost surely, 2^21655788 is an apocalyptic number.

21655788 is a gapful number since it is divisible by the number (28) 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 21655788, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32901120).

21655788 is an abundant number, since it is smaller than the sum of its proper divisors (44146452).

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

21655788 is a wasteful number, since it uses less digits than its factorization.

21655788 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1067 (or 1065 counting only the distinct ones).

The product of its digits is 134400, while the sum is 42.

The square root of 21655788 is about 4653.5779782872. The cubic root of 21655788 is about 278.7348877434.

The spelling of 21655788 in words is "twenty-one million, six hundred fifty-five thousand, seven hundred eighty-eight".