21688747429 has 2 divisors, whose sum is σ = 21688747430. Its totient is φ = 21688747428.

The previous prime is 21688747427. The next prime is 21688747459. The reversal of 21688747429 is 92474788612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14615601025 + 7073146404 = 120895^2 + 84102^2 .

It is a cyclic number.

It is not a de Polignac number, because 21688747429 - 2¹ = 21688747427 is a prime.

It is a super-2 number, since 2×21688747429² (a number of 21 digits) contains 22 as substring.

Together with 21688747427, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21688747427) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10844373714 + 10844373715.

It is an arithmetic number, because the mean of its divisors is an integer number (10844373715).

Almost surely, 2^21688747429 is an apocalyptic number.

It is an amenable number.

21688747429 is a deficient number, since it is larger than the sum of its proper divisors (1).

21688747429 is an equidigital number, since it uses as much as digits as its factorization.

21688747429 is an evil number, because the sum of its binary digits is even.

The product of its digits is 10838016, while the sum is 58.

The spelling of 21688747429 in words is "twenty-one billion, six hundred eighty-eight million, seven hundred forty-seven thousand, four hundred twenty-nine".