21156939 has 6 divisors (see below), whose sum is σ = 30560036. Its totient is φ = 14104620.

The previous prime is 21156931. The next prime is 21156953. The reversal of 21156939 is 93965112.

It is not a de Polignac number, because 21156939 - 2³ = 21156931 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21156931) 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 5 ways as a sum of consecutive naturals, for example, 1175377 + ... + 1175394.

Almost surely, 2^21156939 is an apocalyptic number.

21156939 is a deficient number, since it is larger than the sum of its proper divisors (9403097).

21156939 is a wasteful number, since it uses less digits than its factorization.

21156939 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2350777 (or 2350774 counting only the distinct ones).

The product of its digits is 14580, while the sum is 36.

The square root of 21156939 is about 4599.6672705751. The cubic root of 21156939 is about 276.5779869332.

The spelling of 21156939 in words is "twenty-one million, one hundred fifty-six thousand, nine hundred thirty-nine".