1331999561 has 2 divisors, whose sum is σ = 1331999562. Its totient is φ = 1331999560.

The previous prime is 1331999549. The next prime is 1331999563. The reversal of 1331999561 is 1659991331.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1099254025 + 232745536 = 33155^2 + 15256^2 .

It is an emirp because it is prime and its reverse (1659991331) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1331999561 is a prime.

Together with 1331999563, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (1331999563) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 665999780 + 665999781.

It is an arithmetic number, because the mean of its divisors is an integer number (665999781).

Almost surely, 2^1331999561 is an apocalyptic number.

It is an amenable number.

1331999561 is a deficient number, since it is larger than the sum of its proper divisors (1).

1331999561 is an equidigital number, since it uses as much as digits as its factorization.

1331999561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 196830, while the sum is 47.

The square root of 1331999561 is about 36496.5691675259. The cubic root of 1331999561 is about 1100.2752922551.

The spelling of 1331999561 in words is "one billion, three hundred thirty-one million, nine hundred ninety-nine thousand, five hundred sixty-one".