21605617709 has 16 divisors (see below), whose sum is σ = 24383503872. Its totient is φ = 18994597248.

The previous prime is 21605617703. The next prime is 21605617721. The reversal of 21605617709 is 90771650612.

It is a cyclic number.

It is not a de Polignac number, because 21605617709 - 2¹² = 21605613613 is a prime.

It is a super-3 number, since 3×21605617709³ (a number of 32 digits) contains 333 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21605617709.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21605617703) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 85397 + ... + 224730.

It is an arithmetic number, because the mean of its divisors is an integer number (1523968992).

Almost surely, 2^21605617709 is an apocalyptic number.

It is an amenable number.

21605617709 is a deficient number, since it is larger than the sum of its proper divisors (2777886163).

21605617709 is a wasteful number, since it uses less digits than its factorization.

21605617709 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 310396.

The product of its (nonzero) digits is 158760, while the sum is 44.

The spelling of 21605617709 in words is "twenty-one billion, six hundred five million, six hundred seventeen thousand, seven hundred nine".