21811429781 has 2 divisors, whose sum is σ = 21811429782. Its totient is φ = 21811429780.

The previous prime is 21811429769. The next prime is 21811429819. The reversal of 21811429781 is 18792411812.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14198867281 + 7612562500 = 119159^2 + 87250^2 .

It is a cyclic number.

It is not a de Polignac number, because 21811429781 - 2¹⁴ = 21811413397 is a prime.

It is a super-2 number, since 2×21811429781² (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 (21811429741) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10905714890 + 10905714891.

It is an arithmetic number, because the mean of its divisors is an integer number (10905714891).

Almost surely, 2^21811429781 is an apocalyptic number.

It is an amenable number.

21811429781 is a deficient number, since it is larger than the sum of its proper divisors (1).

21811429781 is an equidigital number, since it uses as much as digits as its factorization.

21811429781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 64512, while the sum is 44.

The spelling of 21811429781 in words is "twenty-one billion, eight hundred eleven million, four hundred twenty-nine thousand, seven hundred eighty-one".