21856437 has 12 divisors (see below), whose sum is σ = 31749120. Its totient is φ = 14488488.

The previous prime is 21856423. The next prime is 21856451. The reversal of 21856437 is 73465812.

21856437 is a `hidden beast` number, since 2 + 1 + 8 + 5 + 643 + 7 = 666.

It is an interprime number because it is at equal distance from previous prime (21856423) and next prime (21856451).

It is not a de Polignac number, because 21856437 - 2²⁰ = 20807861 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21856487) 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, 5173 + ... + 8394.

It is an arithmetic number, because the mean of its divisors is an integer number (2645760).

Almost surely, 2^21856437 is an apocalyptic number.

It is an amenable number.

21856437 is a deficient number, since it is larger than the sum of its proper divisors (9892683).

21856437 is a wasteful number, since it uses less digits than its factorization.

21856437 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13752 (or 13749 counting only the distinct ones).

The product of its digits is 40320, while the sum is 36.

The square root of 21856437 is about 4675.0868441132. The cubic root of 21856437 is about 279.5931037122.

The spelling of 21856437 in words is "twenty-one million, eight hundred fifty-six thousand, four hundred thirty-seven".