21006442 has 4 divisors (see below), whose sum is σ = 31509666. Its totient is φ = 10503220.

The previous prime is 21006439. The next prime is 21006451. The reversal of 21006442 is 24460012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 11215801 + 9790641 = 3349^2 + 3129^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5251609 + ... + 5251612.

Almost surely, 2^21006442 is an apocalyptic number.

21006442 is a deficient number, since it is larger than the sum of its proper divisors (10503224).

21006442 is a wasteful number, since it uses less digits than its factorization.

21006442 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10503223.

The product of its (nonzero) digits is 384, while the sum is 19.

The square root of 21006442 is about 4583.2785208844. The cubic root of 21006442 is about 275.9206258484.

Adding to 21006442 its reverse (24460012), we get a palindrome (45466454).

The spelling of 21006442 in words is "twenty-one million, six thousand, four hundred forty-two".