21235527581 has 2 divisors, whose sum is σ = 21235527582. Its totient is φ = 21235527580.

The previous prime is 21235527571. The next prime is 21235527601. The reversal of 21235527581 is 18572553212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21209261956 + 26265625 = 145634^2 + 5125^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21235527581 is a prime.

It is a super-2 number, since 2×21235527581² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21235527571) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10617763790 + 10617763791.

It is an arithmetic number, because the mean of its divisors is an integer number (10617763791).

Almost surely, 2^21235527581 is an apocalyptic number.

It is an amenable number.

21235527581 is a deficient number, since it is larger than the sum of its proper divisors (1).

21235527581 is an equidigital number, since it uses as much as digits as its factorization.

21235527581 is an evil number, because the sum of its binary digits is even.

The product of its digits is 168000, while the sum is 41.

The spelling of 21235527581 in words is "twenty-one billion, two hundred thirty-five million, five hundred twenty-seven thousand, five hundred eighty-one".