21305424 has 40 divisors (see below), whose sum is σ = 62902720. Its totient is φ = 6087168.

The previous prime is 21305423. The next prime is 21305461. The reversal of 21305424 is 42450312.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a self number, because there is not a number n which added to its sum of digits gives 21305424.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21305423) 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, 31369 + ... + 32040.

It is an arithmetic number, because the mean of its divisors is an integer number (1572568).

Almost surely, 2^21305424 is an apocalyptic number.

21305424 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21305424 is an abundant number, since it is smaller than the sum of its proper divisors (41597296).

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

21305424 is a wasteful number, since it uses less digits than its factorization.

21305424 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 63427 (or 63421 counting only the distinct ones).

The product of its (nonzero) digits is 960, while the sum is 21.

The square root of 21305424 is about 4615.7798907660. The cubic root of 21305424 is about 277.2235116414.

Adding to 21305424 its reverse (42450312), we get a palindrome (63755736).

The spelling of 21305424 in words is "twenty-one million, three hundred five thousand, four hundred twenty-four".