1720665566261 has 4 divisors (see below), whose sum is σ = 1722248516352. Its totient is φ = 1719082616172.

The previous prime is 1720665566251. The next prime is 1720665566311. The reversal of 1720665566261 is 1626655660271.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 1720665566261 - 2¹⁸ = 1720665304117 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1720665566251) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 791473415 + ... + 791475588.

It is an arithmetic number, because the mean of its divisors is an integer number (430562129088).

Almost surely, 2^{1720665566261} is an apocalyptic number.

It is an amenable number.

1720665566261 is a deficient number, since it is larger than the sum of its proper divisors (1582950091).

1720665566261 is a wasteful number, since it uses less digits than its factorization.

1720665566261 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1582950090.

The product of its (nonzero) digits is 5443200, while the sum is 53.

The spelling of 1720665566261 in words is "one trillion, seven hundred twenty billion, six hundred sixty-five million, five hundred sixty-six thousand, two hundred sixty-one".