21505856 has 14 divisors (see below), whose sum is σ = 42675810. Its totient is φ = 10752896.

The previous prime is 21505831. The next prime is 21505859. The reversal of 21505856 is 65850512.

It can be written as a sum of positive squares in only one way, i.e., 17505856 + 4000000 = 4184^2 + 2000^2 .

It is a Harshad number since it is a multiple of its sum of digits (32).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21505859) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 167951 + ... + 168078.

Almost surely, 2^21505856 is an apocalyptic number.

It is an amenable number.

21505856 is a deficient number, since it is larger than the sum of its proper divisors (21169954).

21505856 is an equidigital number, since it uses as much as digits as its factorization.

21505856 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 336041 (or 336031 counting only the distinct ones).

The product of its (nonzero) digits is 12000, while the sum is 32.

The square root of 21505856 is about 4637.4406734750. The cubic root of 21505856 is about 278.0901317395.

The spelling of 21505856 in words is "twenty-one million, five hundred five thousand, eight hundred fifty-six".