19681661 has 2 divisors, whose sum is σ = 19681662. Its totient is φ = 19681660.

The previous prime is 19681639. The next prime is 19681693. The reversal of 19681661 is 16618691.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18438436 + 1243225 = 4294^2 + 1115^2 .

It is an emirp because it is prime and its reverse (16618691) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-19681661 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19681601) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9840830 + 9840831.

It is an arithmetic number, because the mean of its divisors is an integer number (9840831).

Almost surely, 2^19681661 is an apocalyptic number.

It is an amenable number.

19681661 is a deficient number, since it is larger than the sum of its proper divisors (1).

19681661 is an equidigital number, since it uses as much as digits as its factorization.

19681661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 15552, while the sum is 38.

The square root of 19681661 is about 4436.4018077717. The cubic root of 19681661 is about 269.9938773189.

The spelling of 19681661 in words is "nineteen million, six hundred eighty-one thousand, six hundred sixty-one".