21431021081 has 2 divisors, whose sum is σ = 21431021082. Its totient is φ = 21431021080.

The previous prime is 21431021033. The next prime is 21431021113. The reversal of 21431021081 is 18012013412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20243598400 + 1187422681 = 142280^2 + 34459^2 .

It is a cyclic number.

It is not a de Polignac number, because 21431021081 - 2³⁴ = 4251151897 is a prime.

It is a super-2 number, since 2×21431021081² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21431021281) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10715510540 + 10715510541.

It is an arithmetic number, because the mean of its divisors is an integer number (10715510541).

Almost surely, 2^21431021081 is an apocalyptic number.

It is an amenable number.

21431021081 is a deficient number, since it is larger than the sum of its proper divisors (1).

21431021081 is an equidigital number, since it uses as much as digits as its factorization.

21431021081 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 21431021081 its reverse (18012013412), we get a palindrome (39443034493).

The spelling of 21431021081 in words is "twenty-one billion, four hundred thirty-one million, twenty-one thousand, eighty-one".