21240242 has 16 divisors (see below), whose sum is σ = 34007040. Its totient is φ = 9914688.

The previous prime is 21240223. The next prime is 21240251. The reversal of 21240242 is 24204212.

It is a happy number.

It is a super-2 number, since 2×21240242² = 902295760437128, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (17).

It is a self number, because there is not a number n which added to its sum of digits gives 21240242.

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, 1859 + ... + 6777.

It is an arithmetic number, because the mean of its divisors is an integer number (2125440).

Almost surely, 2^21240242 is an apocalyptic number.

21240242 is a deficient number, since it is larger than the sum of its proper divisors (12766798).

21240242 is a wasteful number, since it uses less digits than its factorization.

21240242 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5065.

The product of its (nonzero) digits is 256, while the sum is 17.

The square root of 21240242 is about 4608.7137034101. The cubic root of 21240242 is about 276.9405094953.

Adding to 21240242 its reverse (24204212), we get a palindrome (45444454).

The spelling of 21240242 in words is "twenty-one million, two hundred forty thousand, two hundred forty-two".