21231021281 has 2 divisors, whose sum is σ = 21231021282. Its totient is φ = 21231021280.

The previous prime is 21231021277. The next prime is 21231021337. The reversal of 21231021281 is 18212013212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21228490000 + 2531281 = 145700^2 + 1591^2 .

It is a cyclic number.

It is not a de Polignac number, because 21231021281 - 2² = 21231021277 is a prime.

It is a super-2 number, since 2×21231021281² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21231921281) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10615510640 + 10615510641.

It is an arithmetic number, because the mean of its divisors is an integer number (10615510641).

Almost surely, 2^21231021281 is an apocalyptic number.

It is an amenable number.

21231021281 is a deficient number, since it is larger than the sum of its proper divisors (1).

21231021281 is an equidigital number, since it uses as much as digits as its factorization.

21231021281 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 384, while the sum is 23.

Adding to 21231021281 its reverse (18212013212), we get a palindrome (39443034493).

The spelling of 21231021281 in words is "twenty-one billion, two hundred thirty-one million, twenty-one thousand, two hundred eighty-one".