21554261221 has 4 divisors (see below), whose sum is σ = 21587269932. Its totient is φ = 21521252512.

The previous prime is 21554261203. The next prime is 21554261273. The reversal of 21554261221 is 12216245512.

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

It can be written as a sum of positive squares in 2 ways, for example, as 11035502500 + 10518758721 = 105050^2 + 102561^2 .

It is a cyclic number.

It is not a de Polignac number, because 21554261221 - 2²⁵ = 21520706789 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21554261021) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 16503376 + ... + 16504681.

It is an arithmetic number, because the mean of its divisors is an integer number (5396817483).

Almost surely, 2^21554261221 is an apocalyptic number.

It is an amenable number.

21554261221 is a deficient number, since it is larger than the sum of its proper divisors (33008711).

21554261221 is an equidigital number, since it uses as much as digits as its factorization.

21554261221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 33008710.

The product of its digits is 9600, while the sum is 31.

The spelling of 21554261221 in words is "twenty-one billion, five hundred fifty-four million, two hundred sixty-one thousand, two hundred twenty-one".