21101820 has 48 divisors (see below), whose sum is σ = 60466560. Its totient is φ = 5495616.

The previous prime is 21101819. The next prime is 21101849. The reversal of 21101820 is 2810112.

It is a super-4 number, since 4×21101820⁴ (a number of 30 digits) contains 4444 as substring.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a plaindrome in base 13.

It is a self number, because there is not a number n which added to its sum of digits gives 21101820.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1510 + ... + 6669.

It is an arithmetic number, because the mean of its divisors is an integer number (1259720).

Almost surely, 2^21101820 is an apocalyptic number.

21101820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21101820 is an abundant number, since it is smaller than the sum of its proper divisors (39364740).

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

21101820 is a wasteful number, since it uses less digits than its factorization.

21101820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8234 (or 8232 counting only the distinct ones).

The product of its (nonzero) digits is 32, while the sum is 15.

The square root of 21101820 is about 4593.6717340271. The cubic root of 21101820 is about 276.3375936201.

Adding to 21101820 its reverse (2810112), we get a palindrome (23911932).

The spelling of 21101820 in words is "twenty-one million, one hundred one thousand, eight hundred twenty".