21644693261 has 4 divisors (see below), whose sum is σ = 21918676800. Its totient is φ = 21370709724.

The previous prime is 21644693251. The next prime is 21644693263. The reversal of 21644693261 is 16239644612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21644693261 - 2⁶ = 21644693197 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21644693263) 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, 136991651 + ... + 136991808.

It is an arithmetic number, because the mean of its divisors is an integer number (5479669200).

Almost surely, 2^21644693261 is an apocalyptic number.

It is an amenable number.

21644693261 is a deficient number, since it is larger than the sum of its proper divisors (273983539).

21644693261 is an equidigital number, since it uses as much as digits as its factorization.

21644693261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 273983538.

The product of its digits is 373248, while the sum is 44.

The spelling of 21644693261 in words is "twenty-one billion, six hundred forty-four million, six hundred ninety-three thousand, two hundred sixty-one".