21709623 has 16 divisors (see below), whose sum is σ = 31935456. Its totient is φ = 13032960.

The previous prime is 21709621. The next prime is 21709651. The reversal of 21709623 is 32690712.

It is not a de Polignac number, because 21709623 - 2¹ = 21709621 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21709621) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5190 + ... + 8387.

It is an arithmetic number, because the mean of its divisors is an integer number (1995966).

Almost surely, 2^21709623 is an apocalyptic number.

21709623 is a deficient number, since it is larger than the sum of its proper divisors (10225833).

21709623 is a wasteful number, since it uses less digits than its factorization.

21709623 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13634.

The product of its (nonzero) digits is 4536, while the sum is 30.

The square root of 21709623 is about 4659.3586468526. The cubic root of 21709623 is about 278.9656693926.

The spelling of 21709623 in words is "twenty-one million, seven hundred nine thousand, six hundred twenty-three".