1561866643 has 2 divisors, whose sum is σ = 1561866644. Its totient is φ = 1561866642.

The previous prime is 1561866623. The next prime is 1561866731. The reversal of 1561866643 is 3466681651.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1561866643 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 1561866593 and 1561866602.

It is not a weakly prime, because it can be changed into another prime (1561866623) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 780933321 + 780933322.

It is an arithmetic number, because the mean of its divisors is an integer number (780933322).

Almost surely, 2^1561866643 is an apocalyptic number.

1561866643 is a deficient number, since it is larger than the sum of its proper divisors (1).

1561866643 is an equidigital number, since it uses as much as digits as its factorization.

1561866643 is an evil number, because the sum of its binary digits is even.

The product of its digits is 622080, while the sum is 46.

The square root of 1561866643 is about 39520.4585373196. The cubic root of 1561866643 is about 1160.2403987989.

The spelling of 1561866643 in words is "one billion, five hundred sixty-one million, eight hundred sixty-six thousand, six hundred forty-three".