21721442 has 16 divisors (see below), whose sum is σ = 33929592. Its totient is φ = 10419840.

The previous prime is 21721409. The next prime is 21721457. The reversal of 21721442 is 24412712.

It can be written as a sum of positive squares in 4 ways, for example, as 18412681 + 3308761 = 4291^2 + 1819^2 .

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3392 + ... + 7412.

Almost surely, 2^21721442 is an apocalyptic number.

21721442 is a deficient number, since it is larger than the sum of its proper divisors (12208150).

21721442 is a wasteful number, since it uses less digits than its factorization.

21721442 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4133.

The product of its digits is 896, while the sum is 23.

The square root of 21721442 is about 4660.6267818825. The cubic root of 21721442 is about 279.0162843833.

The spelling of 21721442 in words is "twenty-one million, seven hundred twenty-one thousand, four hundred forty-two".