21991230 has 64 divisors (see below), whose sum is σ = 59443200. Its totient is φ = 5784480.

The previous prime is 21991219. The next prime is 21991231. The reversal of 21991230 is 3219912.

It is a super-2 number, since 2×21991230² = 967228393825800, which contains 22 as substring.

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 = 21991194 and 21991203.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21991231) 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, 20815 + ... + 21845.

It is an arithmetic number, because the mean of its divisors is an integer number (928800).

Almost surely, 2^21991230 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21991230, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29721600).

21991230 is an abundant number, since it is smaller than the sum of its proper divisors (37451970).

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

21991230 is a wasteful number, since it uses less digits than its factorization.

21991230 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1126 (or 1120 counting only the distinct ones).

The product of its (nonzero) digits is 972, while the sum is 27.

The square root of 21991230 is about 4689.4807814938. The cubic root of 21991230 is about 280.1666949580.

The spelling of 21991230 in words is "twenty-one million, nine hundred ninety-one thousand, two hundred thirty".