21711430781 has 2 divisors, whose sum is σ = 21711430782. Its totient is φ = 21711430780.

The previous prime is 21711430693. The next prime is 21711430801. The reversal of 21711430781 is 18703411712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17124077881 + 4587352900 = 130859^2 + 67730^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21711430781 is a prime.

It is a super-2 number, since 2×21711430781² (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 (21711430381) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10855715390 + 10855715391.

It is an arithmetic number, because the mean of its divisors is an integer number (10855715391).

Almost surely, 2^21711430781 is an apocalyptic number.

It is an amenable number.

21711430781 is a deficient number, since it is larger than the sum of its proper divisors (1).

21711430781 is an equidigital number, since it uses as much as digits as its factorization.

21711430781 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 9408, while the sum is 35.

The spelling of 21711430781 in words is "twenty-one billion, seven hundred eleven million, four hundred thirty thousand, seven hundred eighty-one".