21720082 has 4 divisors (see below), whose sum is σ = 32580126. Its totient is φ = 10860040.

The previous prime is 21720053. The next prime is 21720109. The reversal of 21720082 is 28002712.

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

It can be written as a sum of positive squares in only one way, i.e., 19000881 + 2719201 = 4359^2 + 1649^2 .

It is a Smith number, since the sum of its digits (22) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

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 as a sum of consecutive naturals, namely, 5430019 + ... + 5430022.

Almost surely, 2^21720082 is an apocalyptic number.

21720082 is a deficient number, since it is larger than the sum of its proper divisors (10860044).

21720082 is a wasteful number, since it uses less digits than its factorization.

21720082 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10860043.

The product of its (nonzero) digits is 448, while the sum is 22.

The square root of 21720082 is about 4660.4808764762. The cubic root of 21720082 is about 279.0104611041.

Adding to 21720082 its reverse (28002712), we get a palindrome (49722794).

The spelling of 21720082 in words is "twenty-one million, seven hundred twenty thousand, eighty-two".