16681781 has 2 divisors, whose sum is σ = 16681782. Its totient is φ = 16681780.

The previous prime is 16681733. The next prime is 16681787. The reversal of 16681781 is 18718661.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13942756 + 2739025 = 3734^2 + 1655^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-16681781 is a prime.

It is a super-3 number, since 3×16681781³ (a number of 23 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (16681787) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8340890 + 8340891.

It is an arithmetic number, because the mean of its divisors is an integer number (8340891).

Almost surely, 2^16681781 is an apocalyptic number.

It is an amenable number.

16681781 is a deficient number, since it is larger than the sum of its proper divisors (1).

16681781 is an equidigital number, since it uses as much as digits as its factorization.

16681781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 16128, while the sum is 38.

The square root of 16681781 is about 4084.3336053755. Note that the first 3 decimals coincide. The cubic root of 16681781 is about 255.5136691765.

The spelling of 16681781 in words is "sixteen million, six hundred eighty-one thousand, seven hundred eighty-one".