21235427581 has 2 divisors, whose sum is σ = 21235427582. Its totient is φ = 21235427580.

The previous prime is 21235427531. The next prime is 21235427593. The reversal of 21235427581 is 18572453212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18395496900 + 2839930681 = 135630^2 + 53291^2 .

It is a cyclic number.

It is not a de Polignac number, because 21235427581 - 2²⁵ = 21201873149 is a prime.

It is a super-2 number, since 2×21235427581² (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 (21235427531) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10617713790 + 10617713791.

It is an arithmetic number, because the mean of its divisors is an integer number (10617713791).

Almost surely, 2^21235427581 is an apocalyptic number.

It is an amenable number.

21235427581 is a deficient number, since it is larger than the sum of its proper divisors (1).

21235427581 is an equidigital number, since it uses as much as digits as its factorization.

21235427581 is an evil number, because the sum of its binary digits is even.

The product of its digits is 134400, while the sum is 40.

The spelling of 21235427581 in words is "twenty-one billion, two hundred thirty-five million, four hundred twenty-seven thousand, five hundred eighty-one".