21235431281 has 2 divisors, whose sum is σ = 21235431282. Its totient is φ = 21235431280.

The previous prime is 21235431247. The next prime is 21235431307. The reversal of 21235431281 is 18213453212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16554682225 + 4680749056 = 128665^2 + 68416^2 .

It is a cyclic number.

It is not a de Polignac number, because 21235431281 - 2²² = 21231236977 is a prime.

It is a super-2 number, since 2×21235431281² (a number of 21 digits) contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21235431181) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10617715640 + 10617715641.

It is an arithmetic number, because the mean of its divisors is an integer number (10617715641).

Almost surely, 2^21235431281 is an apocalyptic number.

It is an amenable number.

21235431281 is a deficient number, since it is larger than the sum of its proper divisors (1).

21235431281 is an equidigital number, since it uses as much as digits as its factorization.

21235431281 is an evil number, because the sum of its binary digits is even.

The product of its digits is 11520, while the sum is 32.

Adding to 21235431281 its reverse (18213453212), we get a palindrome (39448884493).

The spelling of 21235431281 in words is "twenty-one billion, two hundred thirty-five million, four hundred thirty-one thousand, two hundred eighty-one".