1561720001 has 2 divisors, whose sum is σ = 1561720002. Its totient is φ = 1561720000.

The previous prime is 1561719997. The next prime is 1561720007. The reversal of 1561720001 is 1000271651.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1506604225 + 55115776 = 38815^2 + 7424^2 .

It is a cyclic number.

It is not a de Polignac number, because 1561720001 - 2² = 1561719997 is a prime.

It is not a weakly prime, because it can be changed into another prime (1561720007) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 780860000 + 780860001.

It is an arithmetic number, because the mean of its divisors is an integer number (780860001).

Almost surely, 2^1561720001 is an apocalyptic number.

It is an amenable number.

1561720001 is a deficient number, since it is larger than the sum of its proper divisors (1).

1561720001 is an equidigital number, since it uses as much as digits as its factorization.

1561720001 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 420, while the sum is 23.

The square root of 1561720001 is about 39518.6032268348. The cubic root of 1561720001 is about 1160.2040864162.

Adding to 1561720001 its reverse (1000271651), we get a palindrome (2561991652).

The spelling of 1561720001 in words is "one billion, five hundred sixty-one million, seven hundred twenty thousand, one".