19691561 has 2 divisors, whose sum is σ = 19691562. Its totient is φ = 19691560.

The previous prime is 19691557. The next prime is 19691563. The reversal of 19691561 is 16519691.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13366336 + 6325225 = 3656^2 + 2515^2 .

It is an emirp because it is prime and its reverse (16519691) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 19691561 - 2² = 19691557 is a prime.

Together with 19691563, 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 (19691563) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9845780 + 9845781.

It is an arithmetic number, because the mean of its divisors is an integer number (9845781).

Almost surely, 2^19691561 is an apocalyptic number.

It is an amenable number.

19691561 is a deficient number, since it is larger than the sum of its proper divisors (1).

19691561 is an equidigital number, since it uses as much as digits as its factorization.

19691561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 14580, while the sum is 38.

The square root of 19691561 is about 4437.5174365855. The cubic root of 19691561 is about 270.0391392735.

The spelling of 19691561 in words is "nineteen million, six hundred ninety-one thousand, five hundred sixty-one".