21257609 has 8 divisors (see below), whose sum is σ = 22503360. Its totient is φ = 20046096.

The previous prime is 21257581. The next prime is 21257651. The reversal of 21257609 is 90675212.

21257609 = 682² + 683² + ... + 724².

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 21257609 - 2¹² = 21253513 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21257669) 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, 7277 + ... + 9770.

It is an arithmetic number, because the mean of its divisors is an integer number (2812920).

Almost surely, 2^21257609 is an apocalyptic number.

21257609 is a gapful number since it is divisible by the number (29) formed by its first and last digit.

It is an amenable number.

21257609 is a deficient number, since it is larger than the sum of its proper divisors (1245751).

21257609 is a wasteful number, since it uses less digits than its factorization.

21257609 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17119.

The product of its (nonzero) digits is 7560, while the sum is 32.

The square root of 21257609 is about 4610.5974667065. The cubic root of 21257609 is about 277.0159687041.

The spelling of 21257609 in words is "twenty-one million, two hundred fifty-seven thousand, six hundred nine".