19917281 has 2 divisors, whose sum is σ = 19917282. Its totient is φ = 19917280.

The previous prime is 19917223. The next prime is 19917307. The reversal of 19917281 is 18271991.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15673681 + 4243600 = 3959^2 + 2060^2 .

It is a cyclic number.

It is not a de Polignac number, because 19917281 - 2¹⁸ = 19655137 is a prime.

It is a super-2 number, since 2×19917281² = 793396164865922, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (19917481) by changing a digit.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9958640 + 9958641.

It is an arithmetic number, because the mean of its divisors is an integer number (9958641).

Almost surely, 2^19917281 is an apocalyptic number.

It is an amenable number.

19917281 is a deficient number, since it is larger than the sum of its proper divisors (1).

19917281 is an equidigital number, since it uses as much as digits as its factorization.

19917281 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 9072, while the sum is 38.

The square root of 19917281 is about 4462.8781072308. The cubic root of 19917281 is about 271.0670213632.

The spelling of 19917281 in words is "nineteen million, nine hundred seventeen thousand, two hundred eighty-one".