21720683 has 4 divisors (see below), whose sum is σ = 21891840. Its totient is φ = 21549528.

The previous prime is 21720649. The next prime is 21720689. The reversal of 21720683 is 38602712.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 21720683 - 2⁸ = 21720427 is a prime.

It is a Duffinian number.

It is a plaindrome in base 13.

It is not an unprimeable number, because it can be changed into a prime (21720689) 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, 85388 + ... + 85641.

It is an arithmetic number, because the mean of its divisors is an integer number (5472960).

Almost surely, 2^21720683 is an apocalyptic number.

21720683 is a deficient number, since it is larger than the sum of its proper divisors (171157).

21720683 is a wasteful number, since it uses less digits than its factorization.

21720683 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 171156.

The product of its (nonzero) digits is 4032, while the sum is 29.

The square root of 21720683 is about 4660.5453543550. The cubic root of 21720683 is about 279.0130345096.

The spelling of 21720683 in words is "twenty-one million, seven hundred twenty thousand, six hundred eighty-three".