21105505621 has 4 divisors (see below), whose sum is σ = 21372664000. Its totient is φ = 20838347244.

The previous prime is 21105505609. The next prime is 21105505637. The reversal of 21105505621 is 12650550112.

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 21105505621 - 2⁷ = 21105505493 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21105505621.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21105505721) 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, 133579071 + ... + 133579228.

It is an arithmetic number, because the mean of its divisors is an integer number (5343166000).

Almost surely, 2^21105505621 is an apocalyptic number.

It is an amenable number.

21105505621 is a deficient number, since it is larger than the sum of its proper divisors (267158379).

21105505621 is an equidigital number, since it uses as much as digits as its factorization.

21105505621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 267158378.

The product of its (nonzero) digits is 3000, while the sum is 28.

The spelling of 21105505621 in words is "twenty-one billion, one hundred five million, five hundred five thousand, six hundred twenty-one".