21724090 has 32 divisors (see below), whose sum is σ = 40032144. Its totient is φ = 8486400.

The previous prime is 21724081. The next prime is 21724091. The reversal of 21724090 is 9042712.

It can be written as a sum of positive squares in 8 ways, for example, as 14265729 + 7458361 = 3777^2 + 2731^2 .

It is not an unprimeable number, because it can be changed into a prime (21724091) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 138292 + ... + 138448.

Almost surely, 2^21724090 is an apocalyptic number.

21724090 is a deficient number, since it is larger than the sum of its proper divisors (18308054).

21724090 is a wasteful number, since it uses less digits than its factorization.

21724090 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 402.

The product of its (nonzero) digits is 1008, while the sum is 25.

The square root of 21724090 is about 4660.9108551870. The cubic root of 21724090 is about 279.0276219532.

The spelling of 21724090 in words is "twenty-one million, seven hundred twenty-four thousand, ninety".