21539869 has 8 divisors (see below), whose sum is σ = 23458680. Its totient is φ = 19658496.

The previous prime is 21539839. The next prime is 21539873. The reversal of 21539869 is 96893512.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 2442969 + 19096900 = 1563^2 + 4370^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21539869 - 2⁷ = 21539741 is a prime.

It is a super-2 number, since 2×21539869² = 927931913074322, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21539839) 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 7 ways as a sum of consecutive naturals, for example, 8152 + ... + 10465.

It is an arithmetic number, because the mean of its divisors is an integer number (2932335).

Almost surely, 2^21539869 is an apocalyptic number.

It is an amenable number.

21539869 is a deficient number, since it is larger than the sum of its proper divisors (1918811).

21539869 is a wasteful number, since it uses less digits than its factorization.

21539869 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18719.

The product of its digits is 116640, while the sum is 43.

The square root of 21539869 is about 4641.1064413564. The cubic root of 21539869 is about 278.2366607827.

The spelling of 21539869 in words is "twenty-one million, five hundred thirty-nine thousand, eight hundred sixty-nine".