21123213309 has 48 divisors (see below), whose sum is σ = 34240886784. Its totient is φ = 12435465600.

The previous prime is 21123213263. The next prime is 21123213329. The reversal of 21123213309 is 90331232112.

21123213309 is a `hidden beast` number, since 2 + 1 + 1 + 2 + 321 + 330 + 9 = 666.

It is not a de Polignac number, because 21123213309 - 2²⁰ = 21122164733 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21123213329) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 2387524 + ... + 2396354.

It is an arithmetic number, because the mean of its divisors is an integer number (713351808).

Almost surely, 2^21123213309 is an apocalyptic number.

It is an amenable number.

21123213309 is a deficient number, since it is larger than the sum of its proper divisors (13117673475).

21123213309 is a wasteful number, since it uses less digits than its factorization.

21123213309 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9538 (or 9535 counting only the distinct ones).

The product of its (nonzero) digits is 1944, while the sum is 27.

It can be divided in two parts, 21123 and 213309, that added together give a palindrome (234432).

The spelling of 21123213309 in words is "twenty-one billion, one hundred twenty-three million, two hundred thirteen thousand, three hundred nine".