21242421 has 12 divisors (see below), whose sum is σ = 30988620. Its totient is φ = 14020800.

The previous prime is 21242393. The next prime is 21242443. The reversal of 21242421 is 12424212.

21242421 is a `hidden beast` number, since 2 + 1 + 242 + 421 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 12152196 + 9090225 = 3486^2 + 3015^2 .

It is not a de Polignac number, because 21242421 - 2⁶ = 21242357 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21242394 and 21242403.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21242461) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 10776 + ... + 12593.

It is an arithmetic number, because the mean of its divisors is an integer number (2582385).

Almost surely, 2^21242421 is an apocalyptic number.

It is an amenable number.

21242421 is a deficient number, since it is larger than the sum of its proper divisors (9746199).

21242421 is a wasteful number, since it uses less digits than its factorization.

21242421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23476 (or 23473 counting only the distinct ones).

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

The square root of 21242421 is about 4608.9500973649. The cubic root of 21242421 is about 276.9499794555.

Adding to 21242421 its reverse (12424212), we get a palindrome (33666633).

It can be divided in two parts, 2 and 1242421, that multiplied together give a palindrome (2484842).

The spelling of 21242421 in words is "twenty-one million, two hundred forty-two thousand, four hundred twenty-one".