21521020061 has 2 divisors, whose sum is σ = 21521020062. Its totient is φ = 21521020060.

The previous prime is 21521020033. The next prime is 21521020063. The reversal of 21521020061 is 16002012512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20968488025 + 552532036 = 144805^2 + 23506^2 .

It is a cyclic number.

It is not a de Polignac number, because 21521020061 - 2¹⁴ = 21521003677 is a prime.

It is a Sophie Germain prime.

Together with 21521020063, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21521020063) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10760510030 + 10760510031.

It is an arithmetic number, because the mean of its divisors is an integer number (10760510031).

Almost surely, 2^21521020061 is an apocalyptic number.

It is an amenable number.

21521020061 is a deficient number, since it is larger than the sum of its proper divisors (1).

21521020061 is an equidigital number, since it uses as much as digits as its factorization.

21521020061 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 240, while the sum is 20.

Adding to 21521020061 its reverse (16002012512), we get a palindrome (37523032573).

The spelling of 21521020061 in words is "twenty-one billion, five hundred twenty-one million, twenty thousand, sixty-one".