21042040 has 16 divisors (see below), whose sum is σ = 47344680. Its totient is φ = 8416800.

The previous prime is 21042017. The next prime is 21042053. The reversal of 21042040 is 4024012.

It is a self number, because there is not a number n which added to its sum of digits gives 21042040.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 262986 + ... + 263065.

Almost surely, 2^21042040 is an apocalyptic number.

21042040 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21042040 is an abundant number, since it is smaller than the sum of its proper divisors (26302640).

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

21042040 is a wasteful number, since it uses less digits than its factorization.

21042040 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 526062 (or 526058 counting only the distinct ones).

The product of its (nonzero) digits is 64, while the sum is 13.

The square root of 21042040 is about 4587.1603416493. The cubic root of 21042040 is about 276.0763983703.

Adding to 21042040 its reverse (4024012), we get a palindrome (25066052).

The spelling of 21042040 in words is "twenty-one million, forty-two thousand, forty".