21621644566 has 4 divisors (see below), whose sum is σ = 32432466852. Its totient is φ = 10810822282.

The previous prime is 21621644543. The next prime is 21621644581. The reversal of 21621644566 is 66544612612.

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

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5405411140 + ... + 5405411143.

It is an arithmetic number, because the mean of its divisors is an integer number (8108116713).

Almost surely, 2^21621644566 is an apocalyptic number.

21621644566 is a deficient number, since it is larger than the sum of its proper divisors (10810822286).

21621644566 is a wasteful number, since it uses less digits than its factorization.

21621644566 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10810822285.

The product of its digits is 414720, while the sum is 43.

The spelling of 21621644566 in words is "twenty-one billion, six hundred twenty-one million, six hundred forty-four thousand, five hundred sixty-six".