21531439 has 2 divisors, whose sum is σ = 21531440. Its totient is φ = 21531438.

The previous prime is 21531379. The next prime is 21531443. The reversal of 21531439 is 93413512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21531439 - 2¹⁷ = 21400367 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21531479) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10765719 + 10765720.

It is an arithmetic number, because the mean of its divisors is an integer number (10765720).

Almost surely, 2^21531439 is an apocalyptic number.

21531439 is a deficient number, since it is larger than the sum of its proper divisors (1).

21531439 is an equidigital number, since it uses as much as digits as its factorization.

21531439 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3240, while the sum is 28.

The square root of 21531439 is about 4640.1981638719. The cubic root of 21531439 is about 278.2003584712.

The spelling of 21531439 in words is "twenty-one million, five hundred thirty-one thousand, four hundred thirty-nine".