21109509925 has 18 divisors (see below), whose sum is σ = 30449392818. Its totient is φ = 14475091680.

The previous prime is 21109509901. The next prime is 21109509959. The reversal of 21109509925 is 52990590112.

It can be written as a sum of positive squares in 3 ways, for example, as 2578405284 + 18531104641 = 50778^2 + 136129^2 .

It is not a de Polignac number, because 21109509925 - 2⁷ = 21109509797 is a prime.

It is a super-2 number, since 2×21109509925² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 8614902 + ... + 8617351.

Almost surely, 2^21109509925 is an apocalyptic number.

21109509925 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21109509925 is a deficient number, since it is larger than the sum of its proper divisors (9339882893).

21109509925 is a wasteful number, since it uses less digits than its factorization.

21109509925 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17232277 (or 17232265 counting only the distinct ones).

The product of its (nonzero) digits is 72900, while the sum is 43.

The spelling of 21109509925 in words is "twenty-one billion, one hundred nine million, five hundred nine thousand, nine hundred twenty-five".