21573239 has 2 divisors, whose sum is σ = 21573240. Its totient is φ = 21573238.

The previous prime is 21573203. The next prime is 21573269. The reversal of 21573239 is 93237512.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21573239 is a prime.

It is a super-2 number, since 2×21573239² = 930809281902242, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21573269) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10786619 + 10786620.

It is an arithmetic number, because the mean of its divisors is an integer number (10786620).

Almost surely, 2^21573239 is an apocalyptic number.

21573239 is a deficient number, since it is larger than the sum of its proper divisors (1).

21573239 is an equidigital number, since it uses as much as digits as its factorization.

21573239 is an evil number, because the sum of its binary digits is even.

The product of its digits is 11340, while the sum is 32.

The square root of 21573239 is about 4644.7000979611. The cubic root of 21573239 is about 278.3802699319.

It can be divided in two parts, 21573 and 239, that added together give a palindrome (21812).

The spelling of 21573239 in words is "twenty-one million, five hundred seventy-three thousand, two hundred thirty-nine".