21388609 has 8 divisors (see below), whose sum is σ = 23366880. Its totient is φ = 19416000.

The previous prime is 21388607. The next prime is 21388639. The reversal of 21388609 is 90688312.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21388609 - 2¹ = 21388607 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21388607) 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 7 ways as a sum of consecutive naturals, for example, 12402 + ... + 14020.

It is an arithmetic number, because the mean of its divisors is an integer number (2920860).

Almost surely, 2^21388609 is an apocalyptic number.

It is an amenable number.

21388609 is a deficient number, since it is larger than the sum of its proper divisors (1978271).

21388609 is a wasteful number, since it uses less digits than its factorization.

21388609 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2831.

The product of its (nonzero) digits is 20736, while the sum is 37.

The square root of 21388609 is about 4624.7820489186. The cubic root of 21388609 is about 277.5838406950.

It can be divided in two parts, 2 and 1388609, that added together give a triangular number (1388611 = T₁₆₆₆).

The spelling of 21388609 in words is "twenty-one million, three hundred eighty-eight thousand, six hundred nine".