21521135309 has 2 divisors, whose sum is σ = 21521135310. Its totient is φ = 21521135308.

The previous prime is 21521135287. The next prime is 21521135333. The reversal of 21521135309 is 90353112512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13212812809 + 8308322500 = 114947^2 + 91150^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21521135309 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21521135399) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10760567654 + 10760567655.

It is an arithmetic number, because the mean of its divisors is an integer number (10760567655).

Almost surely, 2^21521135309 is an apocalyptic number.

It is an amenable number.

21521135309 is a deficient number, since it is larger than the sum of its proper divisors (1).

21521135309 is an equidigital number, since it uses as much as digits as its factorization.

21521135309 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 8100, while the sum is 32.

The spelling of 21521135309 in words is "twenty-one billion, five hundred twenty-one million, one hundred thirty-five thousand, three hundred nine".