21056409 has 32 divisors (see below), whose sum is σ = 35143680. Its totient is φ = 12344400.

The previous prime is 21056401. The next prime is 21056437. The reversal of 21056409 is 90465012.

21056409 is a `hidden beast` number, since 2 + 10 + 5 + 640 + 9 = 666.

It is not a de Polignac number, because 21056409 - 2³ = 21056401 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21056401) 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 31 ways as a sum of consecutive naturals, for example, 8064 + ... + 10350.

It is an arithmetic number, because the mean of its divisors is an integer number (1098240).

Almost surely, 2^21056409 is an apocalyptic number.

It is an amenable number.

21056409 is a deficient number, since it is larger than the sum of its proper divisors (14087271).

21056409 is a wasteful number, since it uses less digits than its factorization.

21056409 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2338 (or 2332 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 27.

The square root of 21056409 is about 4588.7262938641. The cubic root of 21056409 is about 276.1392255984.

The spelling of 21056409 in words is "twenty-one million, fifty-six thousand, four hundred nine".