21309620 has 24 divisors (see below), whose sum is σ = 45511200. Its totient is φ = 8378912.

The previous prime is 21309611. The next prime is 21309623. The reversal of 21309620 is 2690312.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21309623) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7850 + ... + 10209.

It is an arithmetic number, because the mean of its divisors is an integer number (1896300).

Almost surely, 2^21309620 is an apocalyptic number.

21309620 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21309620 is an abundant number, since it is smaller than the sum of its proper divisors (24201580).

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

21309620 is a wasteful number, since it uses less digits than its factorization.

21309620 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18127 (or 18125 counting only the distinct ones).

The product of its (nonzero) digits is 648, while the sum is 23.

The square root of 21309620 is about 4616.2343961285. The cubic root of 21309620 is about 277.2417097224.

Adding to 21309620 its reverse (2690312), we get a palindrome (23999932).

The spelling of 21309620 in words is "twenty-one million, three hundred nine thousand, six hundred twenty".