21756330 has 64 divisors (see below), whose sum is σ = 61084800. Its totient is φ = 5495040.

The previous prime is 21756313. The next prime is 21756337. The reversal of 21756330 is 3365712.

It is a happy number.

21756330 is a `hidden beast` number, since 21 + 7 + 5 + 633 + 0 = 666.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21756294 and 21756303.

It is not an unprimeable number, because it can be changed into a prime (21756337) 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, 3010 + ... + 7250.

It is an arithmetic number, because the mean of its divisors is an integer number (954450).

Almost surely, 2^21756330 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21756330, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30542400).

21756330 is an abundant number, since it is smaller than the sum of its proper divisors (39328470).

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

21756330 is a wasteful number, since it uses less digits than its factorization.

21756330 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4276 (or 4270 counting only the distinct ones).

The product of its (nonzero) digits is 3780, while the sum is 27.

The square root of 21756330 is about 4664.3681244087. The cubic root of 21756330 is about 279.1655856001.

The spelling of 21756330 in words is "twenty-one million, seven hundred fifty-six thousand, three hundred thirty".