13138665721 has 2 divisors, whose sum is σ = 13138665722. Its totient is φ = 13138665720.

The previous prime is 13138665719. The next prime is 13138665767. The reversal of 13138665721 is 12756683131.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 7732740096 + 5405925625 = 87936^2 + 73525^2 .

It is a cyclic number.

It is not a de Polignac number, because 13138665721 - 2¹ = 13138665719 is a prime.

Together with 13138665719, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (13138665121) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 6569332860 + 6569332861.

It is an arithmetic number, because the mean of its divisors is an integer number (6569332861).

Almost surely, 2^13138665721 is an apocalyptic number.

It is an amenable number.

13138665721 is a deficient number, since it is larger than the sum of its proper divisors (1).

13138665721 is an equidigital number, since it uses as much as digits as its factorization.

13138665721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 181440, while the sum is 43.

The spelling of 13138665721 in words is "thirteen billion, one hundred thirty-eight million, six hundred sixty-five thousand, seven hundred twenty-one".