21261523 has 4 divisors (see below), whose sum is σ = 21270960. Its totient is φ = 21252088.

The previous prime is 21261517. The next prime is 21261563. The reversal of 21261523 is 32516212.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21261523 - 2²¹ = 19164371 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21261494 and 21261503.

It is not an unprimeable number, because it can be changed into a prime (21261563) 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, 861 + ... + 6577.

It is an arithmetic number, because the mean of its divisors is an integer number (5317740).

Almost surely, 2^21261523 is an apocalyptic number.

21261523 is a deficient number, since it is larger than the sum of its proper divisors (9437).

21261523 is an equidigital number, since it uses as much as digits as its factorization.

21261523 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9436.

The product of its digits is 720, while the sum is 22.

The square root of 21261523 is about 4611.0219040902. The cubic root of 21261523 is about 277.0329692671.

Adding to 21261523 its reverse (32516212), we get a palindrome (53777735).

The spelling of 21261523 in words is "twenty-one million, two hundred sixty-one thousand, five hundred twenty-three".