21721417 has 4 divisors (see below), whose sum is σ = 21831876. Its totient is φ = 21610960.

The previous prime is 21721409. The next prime is 21721457. The reversal of 21721417 is 71412712.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 17816841 + 3904576 = 4221^2 + 1976^2 .

It is a cyclic number.

It is not a de Polignac number, because 21721417 - 2³ = 21721409 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21721391 and 21721400.

It is not an unprimeable number, because it can be changed into a prime (21721457) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 54934 + ... + 55327.

It is an arithmetic number, because the mean of its divisors is an integer number (5457969).

Almost surely, 2^21721417 is an apocalyptic number.

It is an amenable number.

21721417 is a deficient number, since it is larger than the sum of its proper divisors (110459).

21721417 is a wasteful number, since it uses less digits than its factorization.

21721417 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 110458.

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

The square root of 21721417 is about 4660.6240998390. The cubic root of 21721417 is about 279.0161773399.

The spelling of 21721417 in words is "twenty-one million, seven hundred twenty-one thousand, four hundred seventeen".