21861856 has 48 divisors (see below), whose sum is σ = 46463760. Its totient is φ = 10091520.

The previous prime is 21861839. The next prime is 21861859. The reversal of 21861856 is 65816812.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21861859) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 24490 + ... + 25366.

It is an arithmetic number, because the mean of its divisors is an integer number (967995).

Almost surely, 2^21861856 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 21861856, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23231880).

21861856 is an abundant number, since it is smaller than the sum of its proper divisors (24601904).

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

21861856 is a wasteful number, since it uses less digits than its factorization.

21861856 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 947 (or 939 counting only the distinct ones).

The product of its digits is 23040, while the sum is 37.

The square root of 21861856 is about 4675.6663696205. Note that the first 3 decimals coincide. The cubic root of 21861856 is about 279.6162088784.

The spelling of 21861856 in words is "twenty-one million, eight hundred sixty-one thousand, eight hundred fifty-six".