1720661251961 has 2 divisors, whose sum is σ = 1720661251962. Its totient is φ = 1720661251960.

The previous prime is 1720661251949. The next prime is 1720661251993. The reversal of 1720661251961 is 1691521660271.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1098209682025 + 622451569936 = 1047955^2 + 788956^2 .

It is a cyclic number.

It is not a de Polignac number, because 1720661251961 - 2¹⁰ = 1720661250937 is a prime.

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

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 860330625980 + 860330625981.

It is an arithmetic number, because the mean of its divisors is an integer number (860330625981).

Almost surely, 2^{1720661251961} is an apocalyptic number.

It is an amenable number.

1720661251961 is a deficient number, since it is larger than the sum of its proper divisors (1).

1720661251961 is an equidigital number, since it uses as much as digits as its factorization.

1720661251961 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 272160, while the sum is 47.

The spelling of 1720661251961 in words is "one trillion, seven hundred twenty billion, six hundred sixty-one million, two hundred fifty-one thousand, nine hundred sixty-one".