21261547 has 4 divisors (see below), whose sum is σ = 21373056. Its totient is φ = 21150040.

The previous prime is 21261517. The next prime is 21261563. The reversal of 21261547 is 74516212.

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

It is a cyclic number.

It is not a de Polignac number, because 21261547 - 2¹⁹ = 20737259 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21261517) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 55468 + ... + 55849.

It is an arithmetic number, because the mean of its divisors is an integer number (5343264).

Almost surely, 2^21261547 is an apocalyptic number.

21261547 is a deficient number, since it is larger than the sum of its proper divisors (111509).

21261547 is a wasteful number, since it uses less digits than its factorization.

21261547 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 111508.

The product of its digits is 3360, while the sum is 28.

The square root of 21261547 is about 4611.0245065495. The cubic root of 21261547 is about 277.0330735053.

Adding to 21261547 its reverse (74516212), we get a palindrome (95777759).

The spelling of 21261547 in words is "twenty-one million, two hundred sixty-one thousand, five hundred forty-seven".