21720073 has 8 divisors (see below), whose sum is σ = 23277888. Its totient is φ = 20213424.

The previous prime is 21720053. The next prime is 21720109. The reversal of 21720073 is 37002712.

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-21720073 is a prime.

It is a super-2 number, since 2×21720073² = 943523142250658, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21720053) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 11911 + ... + 13612.

It is an arithmetic number, because the mean of its divisors is an integer number (2909736).

Almost surely, 2^21720073 is an apocalyptic number.

21720073 is a gapful number since it is divisible by the number (23) formed by its first and last digit.

It is an amenable number.

21720073 is a deficient number, since it is larger than the sum of its proper divisors (1557815).

21720073 is a wasteful number, since it uses less digits than its factorization.

21720073 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25583.

The product of its (nonzero) digits is 588, while the sum is 22.

The square root of 21720073 is about 4660.4799109105. The cubic root of 21720073 is about 279.0104225668.

Adding to 21720073 its reverse (37002712), we get a palindrome (58722785).

The spelling of 21720073 in words is "twenty-one million, seven hundred twenty thousand, seventy-three".