21409856 has 28 divisors (see below), whose sum is σ = 45755052. Its totient is φ = 9881088.

The previous prime is 21409847. The next prime is 21409867. The reversal of 21409856 is 65890412.

It can be written as a sum of positive squares in 2 ways, for example, as 2190400 + 19219456 = 1480^2 + 4384^2 .

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 12035 + ... + 13698.

It is an arithmetic number, because the mean of its divisors is an integer number (1634109).

Almost surely, 2^21409856 is an apocalyptic number.

21409856 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

It is an amenable number.

21409856 is an abundant number, since it is smaller than the sum of its proper divisors (24345196).

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

21409856 is a wasteful number, since it uses less digits than its factorization.

21409856 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 25758 (or 25748 counting only the distinct ones).

The product of its (nonzero) digits is 17280, while the sum is 35.

The square root of 21409856 is about 4627.0785599555. The cubic root of 21409856 is about 277.6757256171.

The spelling of 21409856 in words is "twenty-one million, four hundred nine thousand, eight hundred fifty-six".