21721046 has 4 divisors (see below), whose sum is σ = 32581572. Its totient is φ = 10860522.

The previous prime is 21721031. The next prime is 21721057. The reversal of 21721046 is 64012712.

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

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5430260 + ... + 5430263.

It is an arithmetic number, because the mean of its divisors is an integer number (8145393).

Almost surely, 2^21721046 is an apocalyptic number.

21721046 is a deficient number, since it is larger than the sum of its proper divisors (10860526).

21721046 is a wasteful number, since it uses less digits than its factorization.

21721046 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10860525.

The product of its (nonzero) digits is 672, while the sum is 23.

The square root of 21721046 is about 4660.5842981326. The cubic root of 21721046 is about 279.0145888065.

Adding to 21721046 its reverse (64012712), we get a palindrome (85733758).

The spelling of 21721046 in words is "twenty-one million, seven hundred twenty-one thousand, forty-six".