16638781 has 2 divisors, whose sum is σ = 16638782. Its totient is φ = 16638780.

The previous prime is 16638751. The next prime is 16638793. The reversal of 16638781 is 18783661.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10830681 + 5808100 = 3291^2 + 2410^2 .

It is a cyclic number.

It is not a de Polignac number, because 16638781 - 2⁵ = 16638749 is a prime.

It is a super-2 number, since 2×16638781² = 553698066331922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (16638731) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8319390 + 8319391.

It is an arithmetic number, because the mean of its divisors is an integer number (8319391).

Almost surely, 2^16638781 is an apocalyptic number.

It is an amenable number.

16638781 is a deficient number, since it is larger than the sum of its proper divisors (1).

16638781 is an equidigital number, since it uses as much as digits as its factorization.

16638781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 48384, while the sum is 40.

The square root of 16638781 is about 4079.0661921572. The cubic root of 16638781 is about 255.2939376093.

The spelling of 16638781 in words is "sixteen million, six hundred thirty-eight thousand, seven hundred eighty-one".