21717421 has 8 divisors (see below), whose sum is σ = 23745888. Its totient is φ = 19698000.

The previous prime is 21717407. The next prime is 21717461. The reversal of 21717421 is 12471712.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21717421 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21717461) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3391 + ... + 7411.

It is an arithmetic number, because the mean of its divisors is an integer number (2968236).

Almost surely, 2^21717421 is an apocalyptic number.

It is an amenable number.

21717421 is a deficient number, since it is larger than the sum of its proper divisors (2028467).

21717421 is a wasteful number, since it uses less digits than its factorization.

21717421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4523.

The product of its digits is 784, while the sum is 25.

The square root of 21717421 is about 4660.1953821702. The cubic root of 21717421 is about 278.9990664700. Note that the first 3 decimals are identical.

It can be divided in two parts, 217174 and 21, that multiplied together give a palindrome (4560654).

The spelling of 21717421 in words is "twenty-one million, seven hundred seventeen thousand, four hundred twenty-one".