21311620 has 48 divisors (see below), whose sum is σ = 49529088. Its totient is φ = 7637760.

The previous prime is 21311611. The next prime is 21311621. The reversal of 21311620 is 2611312.

It is a junction number, because it is equal to n+sod(n) for n = 21311594 and 21311603.

It is not an unprimeable number, because it can be changed into a prime (21311621) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 15397 + ... + 16723.

It is an arithmetic number, because the mean of its divisors is an integer number (1031856).

Almost surely, 2^21311620 is an apocalyptic number.

21311620 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

21311620 is the 2920-th heptagonal number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21311620, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24764544).

21311620 is an abundant number, since it is smaller than the sum of its proper divisors (28217468).

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

21311620 is a wasteful number, since it uses less digits than its factorization.

21311620 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1420 (or 1418 counting only the distinct ones).

The product of its (nonzero) digits is 72, while the sum is 16.

The square root of 21311620 is about 4616.4510178274. The cubic root of 21311620 is about 277.2503828956.

Adding to 21311620 its reverse (2611312), we get a palindrome (23922932).

The spelling of 21311620 in words is "twenty-one million, three hundred eleven thousand, six hundred twenty".