21020421 has 16 divisors (see below), whose sum is σ = 29297664. Its totient is φ = 13392624.

The previous prime is 21020411. The next prime is 21020429. The reversal of 21020421 is 12402012.

It is a de Polignac number, because none of the positive numbers 2^k-21020421 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21020397 and 21020406.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21020429) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4330 + ... + 7796.

It is an arithmetic number, because the mean of its divisors is an integer number (1831104).

Almost surely, 2^21020421 is an apocalyptic number.

It is an amenable number.

21020421 is a deficient number, since it is larger than the sum of its proper divisors (8277243).

21020421 is a wasteful number, since it uses less digits than its factorization.

21020421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3560.

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

The square root of 21020421 is about 4584.8032673169. The cubic root of 21020421 is about 275.9818172227.

Adding to 21020421 its reverse (12402012), we get a palindrome (33422433).

The spelling of 21020421 in words is "twenty-one million, twenty thousand, four hundred twenty-one".