21126913 has 4 divisors (see below), whose sum is σ = 21525588. Its totient is φ = 20728240.

The previous prime is 21126901. The next prime is 21126929. The reversal of 21126913 is 31962112.

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

It can be written as a sum of positive squares in 2 ways, for example, as 13191424 + 7935489 = 3632^2 + 2817^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21126913 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21126943) 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, 199258 + ... + 199363.

It is an arithmetic number, because the mean of its divisors is an integer number (5381397).

Almost surely, 2^21126913 is an apocalyptic number.

It is an amenable number.

21126913 is a deficient number, since it is larger than the sum of its proper divisors (398675).

21126913 is an equidigital number, since it uses as much as digits as its factorization.

21126913 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 398674.

The product of its digits is 648, while the sum is 25.

The square root of 21126913 is about 4596.4021799664. The cubic root of 21126913 is about 276.4470848472.

It can be divided in two parts, 2112 and 6913, that added together give a square (9025 = 95²).

The spelling of 21126913 in words is "twenty-one million, one hundred twenty-six thousand, nine hundred thirteen".