21221533552561 has 2 divisors, whose sum is σ = 21221533552562. Its totient is φ = 21221533552560.

The previous prime is 21221533552529. The next prime is 21221533552577. The reversal of 21221533552561 is 16525533512212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18853997410161 + 2367536142400 = 4342119^2 + 1538680^2 .

It is a cyclic number.

It is not a de Polignac number, because 21221533552561 - 2⁵ = 21221533552529 is a prime.

It is not a weakly prime, because it can be changed into another prime (21221533552591) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10610766776280 + 10610766776281.

It is an arithmetic number, because the mean of its divisors is an integer number (10610766776281).

Almost surely, 2^{21221533552561} is an apocalyptic number.

It is an amenable number.

21221533552561 is a deficient number, since it is larger than the sum of its proper divisors (1).

21221533552561 is an equidigital number, since it uses as much as digits as its factorization.

21221533552561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 540000, while the sum is 43.

The spelling of 21221533552561 in words is "twenty-one trillion, two hundred twenty-one billion, five hundred thirty-three million, five hundred fifty-two thousand, five hundred sixty-one".