21240042 has 16 divisors (see below), whose sum is σ = 42893760. Its totient is φ = 7011072.

The previous prime is 21240001. The next prime is 21240049. The reversal of 21240042 is 24004212.

It is a super-2 number, since 2×21240042² = 902278768323528, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21240049) 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, 16567 + ... + 17802.

It is an arithmetic number, because the mean of its divisors is an integer number (2680860).

Almost surely, 2^21240042 is an apocalyptic number.

21240042 is an abundant number, since it is smaller than the sum of its proper divisors (21653718).

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

21240042 is a wasteful number, since it uses less digits than its factorization.

21240042 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 34477.

The product of its (nonzero) digits is 128, while the sum is 15.

The square root of 21240042 is about 4608.6920053308. The cubic root of 21240042 is about 276.9396402605.

Adding to 21240042 its reverse (24004212), we get a palindrome (45244254).

The spelling of 21240042 in words is "twenty-one million, two hundred forty thousand, forty-two".