21042420021 has 96 divisors (see below), whose sum is σ = 38630711808. Its totient is φ = 10753966080.

The previous prime is 21042419989. The next prime is 21042420031. The reversal of 21042420021 is 12002424012.

21042420021 is a `hidden beast` number, since 21 + 0 + 424 + 200 + 21 = 666.

It is not a de Polignac number, because 21042420021 - 2⁵ = 21042419989 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21042419976 and 21042420003.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21042420031) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 3864661 + ... + 3870101.

It is an arithmetic number, because the mean of its divisors is an integer number (402403248).

Almost surely, 2^21042420021 is an apocalyptic number.

21042420021 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21042420021 is a deficient number, since it is larger than the sum of its proper divisors (17588291787).

21042420021 is a wasteful number, since it uses less digits than its factorization.

21042420021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5651 (or 5648 counting only the distinct ones).

The product of its (nonzero) digits is 256, while the sum is 18.

Adding to 21042420021 its reverse (12002424012), we get a palindrome (33044844033).

The spelling of 21042420021 in words is "twenty-one billion, forty-two million, four hundred twenty thousand, twenty-one".