21309480 has 80 divisors (see below), whose sum is σ = 71634420. Its totient is φ = 5681664.

The previous prime is 21309437. The next prime is 21309487. The reversal of 21309480 is 8490312.

It can be written as a sum of positive squares in 2 ways, for example, as 19766916 + 1542564 = 4446^2 + 1242^2 .

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21309487) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 49 + ... + 6528.

Almost surely, 2^21309480 is an apocalyptic number.

21309480 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21309480, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35817210).

21309480 is an abundant number, since it is smaller than the sum of its proper divisors (50324940).

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

21309480 is a wasteful number, since it uses less digits than its factorization.

21309480 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6600 (or 6587 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 27.

The square root of 21309480 is about 4616.2192322289. The cubic root of 21309480 is about 277.2411025800.

Adding to 21309480 its reverse (8490312), we get a palindrome (29799792).

The spelling of 21309480 in words is "twenty-one million, three hundred nine thousand, four hundred eighty".