21213613257521 has 2 divisors, whose sum is σ = 21213613257522. Its totient is φ = 21213613257520.

The previous prime is 21213613257509. The next prime is 21213613257547. The reversal of 21213613257521 is 12575231631212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13175883619600 + 8037729637921 = 3629860^2 + 2835089^2 .

It is a cyclic number.

It is not a de Polignac number, because 21213613257521 - 2³⁰ = 21212539515697 is a prime.

It is not a weakly prime, because it can be changed into another prime (21213613257721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10606806628760 + 10606806628761.

It is an arithmetic number, because the mean of its divisors is an integer number (10606806628761).

Almost surely, 2^{21213613257521} is an apocalyptic number.

It is an amenable number.

21213613257521 is a deficient number, since it is larger than the sum of its proper divisors (1).

21213613257521 is an equidigital number, since it uses as much as digits as its factorization.

21213613257521 is an evil number, because the sum of its binary digits is even.

The product of its digits is 151200, while the sum is 41.

Adding to 21213613257521 its reverse (12575231631212), we get a palindrome (33788844888733).

The spelling of 21213613257521 in words is "twenty-one trillion, two hundred thirteen billion, six hundred thirteen million, two hundred fifty-seven thousand, five hundred twenty-one".