21621556005221 has 4 divisors (see below), whose sum is σ = 21766667119500. Its totient is φ = 21476444890944.

The previous prime is 21621556005193. The next prime is 21621556005229. The reversal of 21621556005221 is 12250065512612.

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 9171878877121 + 12449677128100 = 3028511^2 + 3528410^2 .

It is a cyclic number.

It is not a de Polignac number, because 21621556005221 - 2⁶ = 21621556005157 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 (21621556005229) 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, 72555556916 + ... + 72555557213.

It is an arithmetic number, because the mean of its divisors is an integer number (5441666779875).

Almost surely, 2^{21621556005221} is an apocalyptic number.

It is an amenable number.

21621556005221 is a deficient number, since it is larger than the sum of its proper divisors (145111114279).

21621556005221 is a wasteful number, since it uses less digits than its factorization.

21621556005221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 145111114278.

The product of its (nonzero) digits is 72000, while the sum is 38.

The spelling of 21621556005221 in words is "twenty-one trillion, six hundred twenty-one billion, five hundred fifty-six million, five thousand, two hundred twenty-one".