21661839 has 12 divisors (see below), whose sum is σ = 32299072. Its totient is φ = 13975200.

The previous prime is 21661831. The next prime is 21661841. The reversal of 21661839 is 93816612.

21661839 is a `hidden beast` number, since 2 + 1 + 6 + 618 + 39 = 666.

It is not a de Polignac number, because 21661839 - 2³ = 21661831 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21661831) 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 11 ways as a sum of consecutive naturals, for example, 38542 + ... + 39099.

Almost surely, 2^21661839 is an apocalyptic number.

21661839 is a deficient number, since it is larger than the sum of its proper divisors (10637233).

21661839 is a wasteful number, since it uses less digits than its factorization.

21661839 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 77678 (or 77675 counting only the distinct ones).

The product of its digits is 15552, while the sum is 36.

The square root of 21661839 is about 4654.2280777805. The cubic root of 21661839 is about 278.7608464346.

It can be divided in two parts, 21661 and 839, that added together give a square (22500 = 150²).

The spelling of 21661839 in words is "twenty-one million, six hundred sixty-one thousand, eight hundred thirty-nine".