21421421 has 4 divisors (see below), whose sum is σ = 24481632. Its totient is φ = 18361212.

The previous prime is 21421399. The next prime is 21421427. The reversal of 21421421 is 12412412.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21421421 - 2¹⁰ = 21420397 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21421421.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21421427) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1530095 + ... + 1530108.

It is an arithmetic number, because the mean of its divisors is an integer number (6120408).

Almost surely, 2^21421421 is an apocalyptic number.

It is an amenable number.

21421421 is a deficient number, since it is larger than the sum of its proper divisors (3060211).

21421421 is an equidigital number, since it uses as much as digits as its factorization.

21421421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3060210.

The product of its digits is 128, while the sum is 17.

The square root of 21421421 is about 4628.3280998650. The cubic root of 21421421 is about 277.7257141476.

Adding to 21421421 its reverse (12412412), we get a palindrome (33833833).

Subtracting from 21421421 its reverse (12412412), we obtain a palindrome (9009009).

The spelling of 21421421 in words is "twenty-one million, four hundred twenty-one thousand, four hundred twenty-one".