21305641 has 12 divisors (see below), whose sum is σ = 26243028. Its totient is φ = 17187072.

The previous prime is 21305639. The next prime is 21305651. The reversal of 21305641 is 14650312.

It can be written as a sum of positive squares in 2 ways, for example, as 7645225 + 13660416 = 2765^2 + 3696^2 .

It is not a de Polignac number, because 21305641 - 2¹ = 21305639 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21305611) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 11956 + ... + 13621.

It is an arithmetic number, because the mean of its divisors is an integer number (2186919).

Almost surely, 2^21305641 is an apocalyptic number.

It is an amenable number.

21305641 is a deficient number, since it is larger than the sum of its proper divisors (4937387).

21305641 is a wasteful number, since it uses less digits than its factorization.

21305641 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 25608 (or 25601 counting only the distinct ones).

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

The square root of 21305641 is about 4615.8033970264. The cubic root of 21305641 is about 277.2244528304.

Adding to 21305641 its reverse (14650312), we get a palindrome (35955953).

The spelling of 21305641 in words is "twenty-one million, three hundred five thousand, six hundred forty-one".