21721610 has 8 divisors (see below), whose sum is σ = 39098916. Its totient is φ = 8688640.

The previous prime is 21721577. The next prime is 21721621. The reversal of 21721610 is 1612712.

It can be written as a sum of positive squares in 2 ways, for example, as 21409129 + 312481 = 4627^2 + 559^2 .

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

It is an unprimeable number.

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 3 ways as a sum of consecutive naturals, for example, 1086071 + ... + 1086090.

Almost surely, 2^21721610 is an apocalyptic number.

21721610 is a deficient number, since it is larger than the sum of its proper divisors (17377306).

21721610 is a wasteful number, since it uses less digits than its factorization.

21721610 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2172168.

The product of its (nonzero) digits is 168, while the sum is 20.

The square root of 21721610 is about 4660.6448051745. The cubic root of 21721610 is about 279.0170037127.

The spelling of 21721610 in words is "twenty-one million, seven hundred twenty-one thousand, six hundred ten".