21081830 has 96 divisors (see below), whose sum is σ = 50561280. Its totient is φ = 6177600.

The previous prime is 21081793. The next prime is 21081833. The reversal of 21081830 is 3818012.

It is a super-2 number, since 2×21081830² = 888887112297800, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21081796 and 21081805.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21081833) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 160865 + ... + 160995.

It is an arithmetic number, because the mean of its divisors is an integer number (526680).

Almost surely, 2^21081830 is an apocalyptic number.

21081830 is an abundant number, since it is smaller than the sum of its proper divisors (29479450).

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

21081830 is a wasteful number, since it uses less digits than its factorization.

21081830 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 186 (or 175 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 23.

The square root of 21081830 is about 4591.4953991047. The cubic root of 21081830 is about 276.2503067774.

Adding to 21081830 its reverse (3818012), we get a palindrome (24899842).

The spelling of 21081830 in words is "twenty-one million, eighty-one thousand, eight hundred thirty".