21501552221 has 4 divisors (see below), whose sum is σ = 22082675292. Its totient is φ = 20920429152.

The previous prime is 21501552211. The next prime is 21501552253. The reversal of 21501552221 is 12225510512.

It is a happy number.

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 15404284996 + 6097267225 = 124114^2 + 78085^2 .

It is a cyclic number.

It is not a de Polignac number, because 21501552221 - 2¹⁴ = 21501535837 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 (21501552211) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 290561480 + ... + 290561553.

It is an arithmetic number, because the mean of its divisors is an integer number (5520668823).

Almost surely, 2^21501552221 is an apocalyptic number.

It is an amenable number.

21501552221 is a deficient number, since it is larger than the sum of its proper divisors (581123071).

21501552221 is an equidigital number, since it uses as much as digits as its factorization.

21501552221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 581123070.

The product of its (nonzero) digits is 2000, while the sum is 26.

The spelling of 21501552221 in words is "twenty-one billion, five hundred one million, five hundred fifty-two thousand, two hundred twenty-one".