21873636 has 72 divisors (see below), whose sum is σ = 58924320. Its totient is φ = 6822144.

The previous prime is 21873629. The next prime is 21873637. The reversal of 21873636 is 63637812.

It is a happy number.

21873636 is a `hidden beast` number, since 2 + 18 + 7 + 3 + 636 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a self number, because there is not a number n which added to its sum of digits gives 21873636.

It is not an unprimeable number, because it can be changed into a prime (21873637) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 77151 + ... + 77433.

Almost surely, 2^21873636 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21873636, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29462160).

21873636 is an abundant number, since it is smaller than the sum of its proper divisors (37050684).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21873636 is a wasteful number, since it uses less digits than its factorization.

21873636 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 425 (or 420 counting only the distinct ones).

The product of its digits is 36288, while the sum is 36.

The square root of 21873636 is about 4676.9259134607. The cubic root of 21873636 is about 279.6664224787. Note that the first 3 decimals are identical.

It can be divided in two parts, 218736 and 36, that multiplied together give a triangular number (7874496 = T₃₉₆₈).

The spelling of 21873636 in words is "twenty-one million, eight hundred seventy-three thousand, six hundred thirty-six".