19997581 has 2 divisors, whose sum is σ = 19997582. Its totient is φ = 19997580.

The previous prime is 19997567. The next prime is 19997591. The reversal of 19997581 is 18579991.

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., 13995081 + 6002500 = 3741^2 + 2450^2 .

It is a cyclic number.

It is not a de Polignac number, because 19997581 - 2⁹ = 19997069 is a prime.

It is a super-2 number, since 2×19997581² = 799806491703122, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19997521) 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, 9998790 + 9998791.

It is an arithmetic number, because the mean of its divisors is an integer number (9998791).

Almost surely, 2^19997581 is an apocalyptic number.

It is an amenable number.

19997581 is a deficient number, since it is larger than the sum of its proper divisors (1).

19997581 is an equidigital number, since it uses as much as digits as its factorization.

19997581 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 204120, while the sum is 49.

The square root of 19997581 is about 4471.8654943994. The cubic root of 19997581 is about 271.4308175912.

The spelling of 19997581 in words is "nineteen million, nine hundred ninety-seven thousand, five hundred eighty-one".