21261647 has 4 divisors (see below), whose sum is σ = 23194536. Its totient is φ = 19328760.

The previous prime is 21261631. The next prime is 21261659. The reversal of 21261647 is 74616212.

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

It is not a de Polignac number, because 21261647 - 2⁴ = 21261631 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21261607) 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, 966428 + ... + 966449.

It is an arithmetic number, because the mean of its divisors is an integer number (5798634).

Almost surely, 2^21261647 is an apocalyptic number.

21261647 is a deficient number, since it is larger than the sum of its proper divisors (1932889).

21261647 is a wasteful number, since it uses less digits than its factorization.

21261647 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1932888.

The product of its digits is 4032, while the sum is 29.

The square root of 21261647 is about 4611.0353501139. The cubic root of 21261647 is about 277.0335078303.

Adding to 21261647 its reverse (74616212), we get a palindrome (95877859).

It can be divided in two parts, 2126 and 1647, that added together give a palindrome (3773).

The spelling of 21261647 in words is "twenty-one million, two hundred sixty-one thousand, six hundred forty-seven".