21311220 has 48 divisors (see below), whose sum is σ = 68197248. Its totient is φ = 4871040.

The previous prime is 21311219. The next prime is 21311237. The reversal of 21311220 is 2211312.

It is a Harshad number since it is a multiple of its sum of digits (12).

It is a junction number, because it is equal to n+sod(n) for n = 21311196 and 21311205.

It is a congruent number.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 24951 + ... + 25790.

It is an arithmetic number, because the mean of its divisors is an integer number (1420776).

Almost surely, 2^21311220 is an apocalyptic number.

21311220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21311220 is an abundant number, since it is smaller than the sum of its proper divisors (46886028).

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

21311220 is a wasteful number, since it uses less digits than its factorization.

21311220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 50760 (or 50758 counting only the distinct ones).

The product of its (nonzero) digits is 24, while the sum is 12.

The square root of 21311220 is about 4616.4076943008. The cubic root of 21311220 is about 277.2486483044.

Adding to 21311220 its reverse (2211312), we get a palindrome (23522532).

The spelling of 21311220 in words is "twenty-one million, three hundred eleven thousand, two hundred twenty".