21539873 has 2 divisors, whose sum is σ = 21539874. Its totient is φ = 21539872.

The previous prime is 21539839. The next prime is 21539879. The reversal of 21539873 is 37893512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16418704 + 5121169 = 4052^2 + 2263^2 .

It is a cyclic number.

It is not a de Polignac number, because 21539873 - 2¹⁰ = 21538849 is a prime.

It is a super-2 number, since 2×21539873² = 927932257712258, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21539879) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10769936 + 10769937.

It is an arithmetic number, because the mean of its divisors is an integer number (10769937).

Almost surely, 2^21539873 is an apocalyptic number.

It is an amenable number.

21539873 is a deficient number, since it is larger than the sum of its proper divisors (1).

21539873 is an equidigital number, since it uses as much as digits as its factorization.

21539873 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 45360, while the sum is 38.

The square root of 21539873 is about 4641.1068722881. The cubic root of 21539873 is about 278.2366780058.

The spelling of 21539873 in words is "twenty-one million, five hundred thirty-nine thousand, eight hundred seventy-three".