21431328781 has 2 divisors, whose sum is σ = 21431328782. Its totient is φ = 21431328780.

The previous prime is 21431328767. The next prime is 21431328839. The reversal of 21431328781 is 18782313412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19639499881 + 1791828900 = 140141^2 + 42330^2 .

It is a cyclic number.

It is not a de Polignac number, because 21431328781 - 2¹¹ = 21431326733 is a prime.

It is a super-2 number, since 2×21431328781² (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 (21431328731) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10715664390 + 10715664391.

It is an arithmetic number, because the mean of its divisors is an integer number (10715664391).

Almost surely, 2^21431328781 is an apocalyptic number.

It is an amenable number.

21431328781 is a deficient number, since it is larger than the sum of its proper divisors (1).

21431328781 is an equidigital number, since it uses as much as digits as its factorization.

21431328781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 64512, while the sum is 40.

The spelling of 21431328781 in words is "twenty-one billion, four hundred thirty-one million, three hundred twenty-eight thousand, seven hundred eighty-one".