1720661251909 has 2 divisors, whose sum is σ = 1720661251910. Its totient is φ = 1720661251908.

The previous prime is 1720661251901. The next prime is 1720661251949. The reversal of 1720661251909 is 9091521660271.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1310459431009 + 410201820900 = 1144753^2 + 640470^2 .

It is an emirp because it is prime and its reverse (9091521660271) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1720661251909 - 2³ = 1720661251901 is a prime.

It is a super-2 number, since 2×1720661251909² (a number of 25 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1720661251901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 860330625954 + 860330625955.

It is an arithmetic number, because the mean of its divisors is an integer number (860330625955).

Almost surely, 2^{1720661251909} is an apocalyptic number.

It is an amenable number.

1720661251909 is a deficient number, since it is larger than the sum of its proper divisors (1).

1720661251909 is an equidigital number, since it uses as much as digits as its factorization.

1720661251909 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 408240, while the sum is 49.

The spelling of 1720661251909 in words is "one trillion, seven hundred twenty billion, six hundred sixty-one million, two hundred fifty-one thousand, nine hundred nine".