21509420 has 48 divisors (see below), whose sum is σ = 49025088. Its totient is φ = 7895040.

The previous prime is 21509419. The next prime is 21509447. The reversal of 21509420 is 2490512.

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, 13169 + ... + 14711.

It is an arithmetic number, because the mean of its divisors is an integer number (1021356).

Almost surely, 2^21509420 is an apocalyptic number.

21509420 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 21509420, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24512544).

21509420 is an abundant number, since it is smaller than the sum of its proper divisors (27515668).

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

21509420 is a wasteful number, since it uses less digits than its factorization.

21509420 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1610 (or 1608 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 23.

The square root of 21509420 is about 4637.8249212319. The cubic root of 21509420 is about 278.1054928034.

Adding to 21509420 its reverse (2490512), we get a palindrome (23999932).

The spelling of 21509420 in words is "twenty-one million, five hundred nine thousand, four hundred twenty".