21531424 has 24 divisors (see below), whose sum is σ = 42785820. Its totient is φ = 10665216.

The previous prime is 21531379. The next prime is 21531439. The reversal of 21531424 is 42413512.

It can be written as a sum of positive squares in 2 ways, for example, as 20250000 + 1281424 = 4500^2 + 1132^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21531395 and 21531404.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 402 + ... + 6574.

Almost surely, 2^21531424 is an apocalyptic number.

It is an amenable number.

21531424 is a deficient number, since it is larger than the sum of its proper divisors (21254396).

21531424 is a wasteful number, since it uses less digits than its factorization.

21531424 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6292 (or 6284 counting only the distinct ones).

The product of its digits is 960, while the sum is 22.

The square root of 21531424 is about 4640.1965475613. The cubic root of 21531424 is about 278.2002938679.

Adding to 21531424 its reverse (42413512), we get a palindrome (63944936).

The spelling of 21531424 in words is "twenty-one million, five hundred thirty-one thousand, four hundred twenty-four".