21042021 has 72 divisors (see below), whose sum is σ = 38942400. Its totient is φ = 10090080.

The previous prime is 21042017. The next prime is 21042053. The reversal of 21042021 is 12024012.

It is not a de Polignac number, because 21042021 - 2² = 21042017 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21041988 and 21042006.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21043021) by changing a digit.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 1618611 + ... + 1618623.

Almost surely, 2^21042021 is an apocalyptic number.

21042021 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21042021 is a deficient number, since it is larger than the sum of its proper divisors (17900379).

21042021 is a wasteful number, since it uses less digits than its factorization.

21042021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 72 (or 34 counting only the distinct ones).

The product of its (nonzero) digits is 32, while the sum is 12.

The square root of 21042021 is about 4587.1582706508. The cubic root of 21042021 is about 276.0763152754.

Adding to 21042021 its reverse (12024012), we get a palindrome (33066033).

Subtracting from 21042021 its reverse (12024012), we obtain a square (9018009 = 3003²).

The spelling of 21042021 in words is "twenty-one million, forty-two thousand, twenty-one".