21573809644 has 6 divisors (see below), whose sum is σ = 37754166884. Its totient is φ = 10786904820.

The previous prime is 21573809641. The next prime is 21573809651. The reversal of 21573809644 is 44690837512.

It is a happy number.

It is not an unprimeable number, because it can be changed into a prime (21573809641) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2696726202 + ... + 2696726209.

It is a 1-persistent number, because it is pandigital, but 2⋅21573809644 = 43147619288 is not.

Almost surely, 2^21573809644 is an apocalyptic number.

It is an amenable number.

21573809644 is a deficient number, since it is larger than the sum of its proper divisors (16180357240).

21573809644 is a wasteful number, since it uses less digits than its factorization.

21573809644 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5393452415 (or 5393452413 counting only the distinct ones).

The product of its (nonzero) digits is 1451520, while the sum is 49.

The spelling of 21573809644 in words is "twenty-one billion, five hundred seventy-three million, eight hundred nine thousand, six hundred forty-four".