21243263665 has 48 divisors (see below), whose sum is σ = 29440454400. Its totient is φ = 14656951296.

The previous prime is 21243263647. The next prime is 21243263669. The reversal of 21243263665 is 56636234212.

It is not a de Polignac number, because 21243263665 - 2¹¹ = 21243261617 is a prime.

It is a super-2 number, since 2×21243263665² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21243263669) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 1991416 + ... + 2002054.

It is an arithmetic number, because the mean of its divisors is an integer number (613342800).

Almost surely, 2^21243263665 is an apocalyptic number.

It is an amenable number.

21243263665 is a deficient number, since it is larger than the sum of its proper divisors (8197190735).

21243263665 is a wasteful number, since it uses less digits than its factorization.

21243263665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10826 (or 10813 counting only the distinct ones).

The product of its digits is 311040, while the sum is 40.

Adding to 21243263665 its reverse (56636234212), we get a palindrome (77879497877).

The spelling of 21243263665 in words is "twenty-one billion, two hundred forty-three million, two hundred sixty-three thousand, six hundred sixty-five".