21531421 has 4 divisors (see below), whose sum is σ = 21550144. Its totient is φ = 21512700.

The previous prime is 21531379. The next prime is 21531439. The reversal of 21531421 is 12413512.

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 21531421 - 2⁹ = 21530909 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21531481) 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 3 ways as a sum of consecutive naturals, for example, 7515 + ... + 9976.

It is an arithmetic number, because the mean of its divisors is an integer number (5387536).

Almost surely, 2^21531421 is an apocalyptic number.

It is an amenable number.

21531421 is a deficient number, since it is larger than the sum of its proper divisors (18723).

21531421 is a wasteful number, since it uses less digits than its factorization.

21531421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18722.

The product of its digits is 240, while the sum is 19.

The square root of 21531421 is about 4640.1962242991. The cubic root of 21531421 is about 278.2002809472.

Adding to 21531421 its reverse (12413512), we get a palindrome (33944933).

It can be divided in two parts, 21531 and 421, that added together give a cube (21952 = 28³).

The spelling of 21531421 in words is "twenty-one million, five hundred thirty-one thousand, four hundred twenty-one".