21005842 has 32 divisors (see below), whose sum is σ = 37384704. Its totient is φ = 8799120.

The previous prime is 21005837. The next prime is 21005857. The reversal of 21005842 is 24850012.

It is a Harshad number since it is a multiple of its sum of digits (22).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 34303 + ... + 34909.

It is an arithmetic number, because the mean of its divisors is an integer number (1168272).

Almost surely, 2^21005842 is an apocalyptic number.

21005842 is a gapful number since it is divisible by the number (22) formed by its first and last digit.

21005842 is a deficient number, since it is larger than the sum of its proper divisors (16378862).

21005842 is a wasteful number, since it uses less digits than its factorization.

21005842 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 655 (or 633 counting only the distinct ones).

The product of its (nonzero) digits is 640, while the sum is 22.

The square root of 21005842 is about 4583.2130650887. The cubic root of 21005842 is about 275.9179988138.

Adding to 21005842 its reverse (24850012), we get a palindrome (45855854).

The spelling of 21005842 in words is "twenty-one million, five thousand, eight hundred forty-two".