21381820 has 24 divisors (see below), whose sum is σ = 45250128. Its totient is φ = 8486400.

The previous prime is 21381791. The next prime is 21381823. The reversal of 21381820 is 2818312.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21381823) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 1461 + ... + 6700.

It is an arithmetic number, because the mean of its divisors is an integer number (1885422).

Almost surely, 2^21381820 is an apocalyptic number.

21381820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21381820 is an abundant number, since it is smaller than the sum of its proper divisors (23868308).

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

21381820 is a wasteful number, since it uses less digits than its factorization.

21381820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8301 (or 8299 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 25.

The square root of 21381820 is about 4624.0480101314. The cubic root of 21381820 is about 277.5544681113.

It can be divided in two parts, 21381 and 820, that added together give a square (22201 = 149²).

The spelling of 21381820 in words is "twenty-one million, three hundred eighty-one thousand, eight hundred twenty".