21531379 has 2 divisors, whose sum is σ = 21531380. Its totient is φ = 21531378.

The previous prime is 21531361. The next prime is 21531439. The reversal of 21531379 is 97313512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21531379 - 2⁹ = 21530867 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21531379.

It is not a weakly prime, because it can be changed into another prime (21531179) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10765689 + 10765690.

It is an arithmetic number, because the mean of its divisors is an integer number (10765690).

Almost surely, 2^21531379 is an apocalyptic number.

21531379 is a deficient number, since it is larger than the sum of its proper divisors (1).

21531379 is an equidigital number, since it uses as much as digits as its factorization.

21531379 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5670, while the sum is 31.

The square root of 21531379 is about 4640.1916986263. The cubic root of 21531379 is about 278.2001000578.

The spelling of 21531379 in words is "twenty-one million, five hundred thirty-one thousand, three hundred seventy-nine".